diff --git a/CHANGELOG.md b/CHANGELOG.md
index c879685c..d9d52685 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -35,6 +35,10 @@ Check our main [developer changelog](https://developer.paddle.com/?utm_source=dx
 - `paddle_billing.Entities.Event` `data` will now be `paddle_billing.Notifications.Entities.UndefinedEntity` for unknown event types
 - `paddle_billing.Resources.Reports.Operations.CreateReport` is replaced by report specific operations `CreateAdjustmentsReport` | `CreateDiscountsReport` | `CreateProductsAndPricesReport` | `CreateTransactionsReport`
 - `paddle_billing.Entities.Notification` `payload` is now `paddle_billing.Entities.Notifications.NotificationEvent`
+- `paddle_billing.Entities.Shared.BillingDetails` is no longer used for `billing_details` in request operations
+  - `CreateTransaction` now uses `paddle_billing.Resources.Transactions.Operations.Create.CreateBillingDetails`
+  - `UpdateTransaction` now uses `paddle_billing.Resources.Transactions.Operations.Update.UpdateBillingDetails`
+  - `UpdateSubscription` | `PreviewUpdateSubscription` now uses `paddle_billing.Resources.Subscriptions.Operations.Update.UpdateBillingDetails`
 
 ### Fixed
 
diff --git a/UPGRADING.md b/UPGRADING.md
index d1187a04..f2181d2f 100644
--- a/UPGRADING.md
+++ b/UPGRADING.md
@@ -50,6 +50,13 @@ Usage of `paddle_billing.Resources.Reports.Operations.CreateReport` should be re
 - `paddle_billing.Resources.Reports.Operations.CreateProductsAndPricesReport`
 - `paddle_billing.Resources.Reports.Operations.CreateTransactionsReport`
 
+### 5. `BillingDetails` entity is no longer used for `billing_details` in request operations
+
+Usage of `paddle_billing.Entities.Shared.BillingDetails` for `billing_details` in request operations, should be replaced with:
+- `paddle_billing.Resources.Transactions.Operations.Create.CreateBillingDetails` for `CreateTransaction`
+- `paddle_billing.Resources.Transactions.Operations.Update.UpdateBillingDetails` for `UpdateTransaction`
+- `paddle_billing.Resources.Subscriptions.Operations.Update.UpdateBillingDetails` for `UpdateSubscription` | `PreviewUpdateSubscription`
+
 ## v0.2.0
 
 This release includes a few breaking changes. These changes should be limited impact on most integrations but may cause problems in some circumstances. 
diff --git a/paddle_billing/Client.py b/paddle_billing/Client.py
index 5a588ab0..72d23d8a 100644
--- a/paddle_billing/Client.py
+++ b/paddle_billing/Client.py
@@ -5,8 +5,11 @@
 from urllib3.util.retry import Retry
 from urllib.parse import urljoin, urlencode
 from uuid import uuid4
+from dataclasses import fields, is_dataclass
 
+from paddle_billing.Operation import Operation
 from paddle_billing.FiltersUndefined import FiltersUndefined
+from paddle_billing.Undefined import Undefined
 from paddle_billing.HasParameters import HasParameters
 from paddle_billing.Options import Options
 from paddle_billing.ResponseParser import ResponseParser
@@ -34,6 +37,16 @@
 
 class PayloadEncoder(JSONEncoder):
     def default(self, z):
+        if is_dataclass(z):
+            data = {}
+            for field in fields(z):
+                data[field.name] = getattr(z, field.name)
+
+            return FiltersUndefined.filter_undefined_values(data)
+
+        if isinstance(z, Undefined):
+            return None
+
         if hasattr(z, "to_json") and callable(z.to_json):
             return z.to_json()
 
@@ -105,7 +118,7 @@ def logging_hook(self, response, *args, **kwargs):
         self.log.debug(f"Response: {response.status_code} {response.text}")
 
     @staticmethod
-    def serialize_json_payload(payload: dict) -> str:
+    def serialize_json_payload(payload: dict | Operation) -> str:
         json_payload = json_dumps(payload, cls=PayloadEncoder)
         final_json = json_payload if json_payload != "[]" else "{}"
 
@@ -115,7 +128,7 @@ def _make_request(
         self,
         method: str,
         url: str,
-        payload: dict | None = None,
+        payload: dict | Operation | None = None,
     ) -> Response:
         """
         Makes an actual API call to Paddle
@@ -168,17 +181,17 @@ def get_raw(self, url: str, parameters: HasParameters | dict = None) -> Response
         return self._make_request("GET", url, None)
 
     def post_raw(
-        self, url: str, payload: dict | None = None, parameters: HasParameters | dict | None = None
+        self, url: str, payload: dict | Operation | None = None, parameters: HasParameters | dict | None = None
     ) -> Response:
-        if payload:
+        if isinstance(payload, dict):
             payload = FiltersUndefined.filter_undefined_values(payload)  # Strip Undefined items from the dict
 
         url = Client.format_uri_parameters(url, parameters) if parameters else url
 
         return self._make_request("POST", url, payload)
 
-    def patch_raw(self, url: str, payload: dict | None) -> Response:
-        if payload:
+    def patch_raw(self, url: str, payload: dict | Operation | None) -> Response:
+        if isinstance(payload, dict):
             payload = FiltersUndefined.filter_undefined_values(payload)  # Strip Undefined items from the dict
 
         return self._make_request("PATCH", url, payload)
diff --git a/paddle_billing/Entities/DateTime.py b/paddle_billing/Entities/DateTime.py
index 85a66604..dd87aca4 100644
--- a/paddle_billing/Entities/DateTime.py
+++ b/paddle_billing/Entities/DateTime.py
@@ -36,3 +36,6 @@ def from_datetime(cls, date: datetime | str):
 
     def __str__(self):
         return self.format()
+
+    def to_json(self):
+        return self.format()
diff --git a/paddle_billing/Entities/Shared/BillingDetailsUpdate.py b/paddle_billing/Entities/Shared/BillingDetailsUpdate.py
deleted file mode 100644
index 3b46fb29..00000000
--- a/paddle_billing/Entities/Shared/BillingDetailsUpdate.py
+++ /dev/null
@@ -1,21 +0,0 @@
-from __future__ import annotations
-from dataclasses import dataclass
-
-from paddle_billing.Entities.Shared.TimePeriod import TimePeriod
-
-
-@dataclass
-class BillingDetailsUpdate:
-    enable_checkout: bool
-    purchase_order_number: str
-    additional_information: str
-    payment_terms: TimePeriod
-
-    @staticmethod
-    def from_dict(data: dict) -> BillingDetailsUpdate:
-        return BillingDetailsUpdate(
-            enable_checkout=data["enable_checkout"],
-            purchase_order_number=data["purchase_order_number"],
-            additional_information=data["additional_information"],
-            payment_terms=TimePeriod.from_dict(data["payment_terms"]),
-        )
diff --git a/paddle_billing/Entities/Shared/__init__.py b/paddle_billing/Entities/Shared/__init__.py
index 3ff1cbeb..6e2bd6e6 100644
--- a/paddle_billing/Entities/Shared/__init__.py
+++ b/paddle_billing/Entities/Shared/__init__.py
@@ -5,7 +5,6 @@
 from paddle_billing.Entities.Shared.AdjustmentTotals import AdjustmentTotals
 from paddle_billing.Entities.Shared.AdjustmentType import AdjustmentType
 from paddle_billing.Entities.Shared.BillingDetails import BillingDetails
-from paddle_billing.Entities.Shared.BillingDetailsUpdate import BillingDetailsUpdate
 from paddle_billing.Entities.Shared.Card import Card
 from paddle_billing.Entities.Shared.CatalogType import CatalogType
 from paddle_billing.Entities.Shared.ChargebackFee import ChargebackFee
diff --git a/paddle_billing/Operation.py b/paddle_billing/Operation.py
new file mode 100644
index 00000000..e66cd3d6
--- /dev/null
+++ b/paddle_billing/Operation.py
@@ -0,0 +1,7 @@
+from abc import ABC
+from dataclasses import dataclass
+
+
+@dataclass
+class Operation(ABC):
+    pass
diff --git a/paddle_billing/Resources/Subscriptions/Operations/PreviewUpdateSubscription.py b/paddle_billing/Resources/Subscriptions/Operations/PreviewUpdateSubscription.py
index 0c595b4b..35c5b6f2 100644
--- a/paddle_billing/Resources/Subscriptions/Operations/PreviewUpdateSubscription.py
+++ b/paddle_billing/Resources/Subscriptions/Operations/PreviewUpdateSubscription.py
@@ -1,9 +1,10 @@
-from dataclasses import asdict, dataclass
+from dataclasses import dataclass
 
+from paddle_billing.Operation import Operation
 from paddle_billing.Undefined import Undefined
 
 from paddle_billing.Entities.DateTime import DateTime
-from paddle_billing.Entities.Shared import BillingDetails, CollectionMode, CurrencyCode, CustomData
+from paddle_billing.Entities.Shared import CollectionMode, CurrencyCode, CustomData
 from paddle_billing.Entities.Subscriptions import (
     SubscriptionItems,
     SubscriptionItemsWithPrice,
@@ -11,11 +12,14 @@
     SubscriptionProrationBillingMode,
 )
 
-from paddle_billing.Resources.Subscriptions.Operations.Update.SubscriptionDiscount import SubscriptionDiscount
+from paddle_billing.Resources.Subscriptions.Operations.Update import (
+    SubscriptionDiscount,
+    UpdateBillingDetails,
+)
 
 
 @dataclass
-class PreviewUpdateSubscription:
+class PreviewUpdateSubscription(Operation):
     customer_id: str | Undefined = Undefined()
     address_id: str | Undefined = Undefined()
     business_id: str | None | Undefined = Undefined()
@@ -23,19 +27,9 @@ class PreviewUpdateSubscription:
     next_billed_at: DateTime | Undefined = Undefined()
     discount: SubscriptionDiscount | None | Undefined = Undefined()
     collection_mode: CollectionMode | Undefined = Undefined()
-    billing_details: BillingDetails | None | Undefined = Undefined()
+    billing_details: UpdateBillingDetails | None | Undefined = Undefined()
     scheduled_change: None | Undefined = Undefined()
     items: list[SubscriptionItems | SubscriptionItemsWithPrice] | Undefined = Undefined()
     custom_data: CustomData | None | Undefined = Undefined()
     proration_billing_mode: SubscriptionProrationBillingMode | Undefined = Undefined()
     on_payment_failure: SubscriptionOnPaymentFailure | Undefined = Undefined()
-
-    def get_parameters(self) -> dict:
-        parameters = asdict(self)
-
-        if isinstance(self.next_billed_at, DateTime):
-            parameters["next_billed_at"] = self.next_billed_at.format()
-        if not isinstance(self.items, Undefined):
-            parameters["items"] = [item.get_parameters() for item in self.items]
-
-        return parameters
diff --git a/paddle_billing/Resources/Subscriptions/Operations/Update/UpdateBillingDetails.py b/paddle_billing/Resources/Subscriptions/Operations/Update/UpdateBillingDetails.py
new file mode 100644
index 00000000..d09bf523
--- /dev/null
+++ b/paddle_billing/Resources/Subscriptions/Operations/Update/UpdateBillingDetails.py
@@ -0,0 +1,13 @@
+from __future__ import annotations
+from dataclasses import dataclass
+
+from paddle_billing.Entities.Shared.Duration import Duration
+from paddle_billing.Undefined import Undefined
+
+
+@dataclass
+class UpdateBillingDetails:
+    payment_terms: Duration | Undefined = Undefined()
+    enable_checkout: bool | Undefined = Undefined()
+    purchase_order_number: str | Undefined = Undefined()
+    additional_information: str | None | Undefined = Undefined()
diff --git a/paddle_billing/Resources/Subscriptions/Operations/Update/__init__.py b/paddle_billing/Resources/Subscriptions/Operations/Update/__init__.py
index e69de29b..3033e756 100644
--- a/paddle_billing/Resources/Subscriptions/Operations/Update/__init__.py
+++ b/paddle_billing/Resources/Subscriptions/Operations/Update/__init__.py
@@ -0,0 +1,2 @@
+from paddle_billing.Resources.Subscriptions.Operations.Update.SubscriptionDiscount import SubscriptionDiscount
+from paddle_billing.Resources.Subscriptions.Operations.Update.UpdateBillingDetails import UpdateBillingDetails
diff --git a/paddle_billing/Resources/Subscriptions/Operations/UpdateSubscription.py b/paddle_billing/Resources/Subscriptions/Operations/UpdateSubscription.py
index d8c1da63..2139f6a6 100644
--- a/paddle_billing/Resources/Subscriptions/Operations/UpdateSubscription.py
+++ b/paddle_billing/Resources/Subscriptions/Operations/UpdateSubscription.py
@@ -1,9 +1,10 @@
-from dataclasses import asdict, dataclass
+from dataclasses import dataclass
 
+from paddle_billing.Operation import Operation
 from paddle_billing.Undefined import Undefined
 
 from paddle_billing.Entities.DateTime import DateTime
-from paddle_billing.Entities.Shared import BillingDetails, CollectionMode, CurrencyCode, CustomData
+from paddle_billing.Entities.Shared import CollectionMode, CurrencyCode, CustomData
 from paddle_billing.Entities.Subscriptions import (
     SubscriptionItems,
     SubscriptionItemsWithPrice,
@@ -11,11 +12,14 @@
     SubscriptionProrationBillingMode,
 )
 
-from paddle_billing.Resources.Subscriptions.Operations.Update.SubscriptionDiscount import SubscriptionDiscount
+from paddle_billing.Resources.Subscriptions.Operations.Update import (
+    SubscriptionDiscount,
+    UpdateBillingDetails,
+)
 
 
 @dataclass
-class UpdateSubscription:
+class UpdateSubscription(Operation):
     customer_id: str | Undefined = Undefined()
     address_id: str | Undefined = Undefined()
     business_id: str | None | Undefined = Undefined()
@@ -23,19 +27,9 @@ class UpdateSubscription:
     next_billed_at: DateTime | Undefined = Undefined()
     discount: SubscriptionDiscount | None | Undefined = Undefined()
     collection_mode: CollectionMode | Undefined = Undefined()
-    billing_details: BillingDetails | None | Undefined = Undefined()
+    billing_details: UpdateBillingDetails | None | Undefined = Undefined()
     scheduled_change: None | Undefined = Undefined()
     items: list[SubscriptionItems | SubscriptionItemsWithPrice] | Undefined = Undefined()
     custom_data: CustomData | None | Undefined = Undefined()
     proration_billing_mode: SubscriptionProrationBillingMode | Undefined = Undefined()
     on_payment_failure: SubscriptionOnPaymentFailure | Undefined = Undefined()
-
-    def get_parameters(self) -> dict:
-        parameters = asdict(self)
-
-        if isinstance(self.next_billed_at, DateTime):
-            parameters["next_billed_at"] = self.next_billed_at.format()
-        if not isinstance(self.items, Undefined):
-            parameters["items"] = [item.get_parameters() for item in self.items]
-
-        return parameters
diff --git a/paddle_billing/Resources/Subscriptions/SubscriptionsClient.py b/paddle_billing/Resources/Subscriptions/SubscriptionsClient.py
index 8d379a9c..4348d2f0 100644
--- a/paddle_billing/Resources/Subscriptions/SubscriptionsClient.py
+++ b/paddle_billing/Resources/Subscriptions/SubscriptionsClient.py
@@ -58,7 +58,7 @@ def get(self, subscription_id: str, includes=None) -> Subscription:
         return Subscription.from_dict(parser.get_data())
 
     def update(self, subscription_id: str, operation: UpdateSubscription) -> Subscription:
-        self.response = self.client.patch_raw(f"/subscriptions/{subscription_id}", operation.get_parameters())
+        self.response = self.client.patch_raw(f"/subscriptions/{subscription_id}", operation)
         parser = ResponseParser(self.response)
 
         return Subscription.from_dict(parser.get_data())
@@ -100,7 +100,7 @@ def create_one_time_charge(self, subscription_id: str, operation: CreateOneTimeC
         return Subscription.from_dict(parser.get_data())
 
     def preview_update(self, subscription_id: str, operation: PreviewUpdateSubscription) -> SubscriptionPreview:
-        self.response = self.client.patch_raw(f"/subscriptions/{subscription_id}/preview", operation.get_parameters())
+        self.response = self.client.patch_raw(f"/subscriptions/{subscription_id}/preview", operation)
         parser = ResponseParser(self.response)
 
         return SubscriptionPreview.from_dict(parser.get_data())
diff --git a/paddle_billing/Resources/Transactions/Operations/Create/CreateBillingDetails.py b/paddle_billing/Resources/Transactions/Operations/Create/CreateBillingDetails.py
new file mode 100644
index 00000000..e446760a
--- /dev/null
+++ b/paddle_billing/Resources/Transactions/Operations/Create/CreateBillingDetails.py
@@ -0,0 +1,13 @@
+from __future__ import annotations
+from dataclasses import dataclass
+
+from paddle_billing.Entities.Shared.Duration import Duration
+from paddle_billing.Undefined import Undefined
+
+
+@dataclass
+class CreateBillingDetails:
+    payment_terms: Duration
+    enable_checkout: bool | Undefined = Undefined()
+    purchase_order_number: str | Undefined = Undefined()
+    additional_information: str | None | Undefined = Undefined()
diff --git a/paddle_billing/Resources/Transactions/Operations/Create/__init__.py b/paddle_billing/Resources/Transactions/Operations/Create/__init__.py
new file mode 100644
index 00000000..d379e8a1
--- /dev/null
+++ b/paddle_billing/Resources/Transactions/Operations/Create/__init__.py
@@ -0,0 +1 @@
+from paddle_billing.Resources.Transactions.Operations.Create.CreateBillingDetails import CreateBillingDetails
diff --git a/paddle_billing/Resources/Transactions/Operations/CreateTransaction.py b/paddle_billing/Resources/Transactions/Operations/CreateTransaction.py
index 37ad0c54..9a996053 100644
--- a/paddle_billing/Resources/Transactions/Operations/CreateTransaction.py
+++ b/paddle_billing/Resources/Transactions/Operations/CreateTransaction.py
@@ -1,8 +1,8 @@
-from dataclasses import asdict, dataclass
+from dataclasses import dataclass
 
+from paddle_billing.Operation import Operation
 from paddle_billing.Undefined import Undefined
 from paddle_billing.Entities.Shared import (
-    BillingDetails,
     Checkout,
     CollectionMode,
     CurrencyCode,
@@ -11,11 +11,12 @@
     TransactionStatus,
 )
 from paddle_billing.Entities.Transactions import TransactionCreateItem, TransactionCreateItemWithPrice
+from paddle_billing.Resources.Transactions.Operations.Create import CreateBillingDetails
 
 
 @dataclass
-class CreateTransaction:
-    items: list[TransactionCreateItem | TransactionCreateItemWithPrice] = Undefined()
+class CreateTransaction(Operation):
+    items: list[TransactionCreateItem | TransactionCreateItemWithPrice]
     status: TransactionStatus | Undefined = Undefined()
     customer_id: str | None | Undefined = Undefined()
     address_id: str | None | Undefined = Undefined()
@@ -24,9 +25,6 @@ class CreateTransaction:
     currency_code: CurrencyCode | Undefined = Undefined()
     collection_mode: CollectionMode | Undefined = Undefined()
     discount_id: str | None | Undefined = Undefined()
-    billing_details: BillingDetails | None | Undefined = Undefined()
+    billing_details: CreateBillingDetails | None | Undefined = Undefined()
     billing_period: TimePeriod | None | Undefined = Undefined()
     checkout: Checkout | None | Undefined = Undefined()
-
-    def get_parameters(self) -> dict:
-        return asdict(self)
diff --git a/paddle_billing/Resources/Transactions/Operations/Update/UpdateBillingDetails.py b/paddle_billing/Resources/Transactions/Operations/Update/UpdateBillingDetails.py
new file mode 100644
index 00000000..d09bf523
--- /dev/null
+++ b/paddle_billing/Resources/Transactions/Operations/Update/UpdateBillingDetails.py
@@ -0,0 +1,13 @@
+from __future__ import annotations
+from dataclasses import dataclass
+
+from paddle_billing.Entities.Shared.Duration import Duration
+from paddle_billing.Undefined import Undefined
+
+
+@dataclass
+class UpdateBillingDetails:
+    payment_terms: Duration | Undefined = Undefined()
+    enable_checkout: bool | Undefined = Undefined()
+    purchase_order_number: str | Undefined = Undefined()
+    additional_information: str | None | Undefined = Undefined()
diff --git a/paddle_billing/Resources/Transactions/Operations/Update/__init__.py b/paddle_billing/Resources/Transactions/Operations/Update/__init__.py
new file mode 100644
index 00000000..37aec216
--- /dev/null
+++ b/paddle_billing/Resources/Transactions/Operations/Update/__init__.py
@@ -0,0 +1 @@
+from paddle_billing.Resources.Transactions.Operations.Update.UpdateBillingDetails import UpdateBillingDetails
diff --git a/paddle_billing/Resources/Transactions/Operations/UpdateTransaction.py b/paddle_billing/Resources/Transactions/Operations/UpdateTransaction.py
index 493ee590..bd8dbc60 100644
--- a/paddle_billing/Resources/Transactions/Operations/UpdateTransaction.py
+++ b/paddle_billing/Resources/Transactions/Operations/UpdateTransaction.py
@@ -1,8 +1,8 @@
-from dataclasses import asdict, dataclass
+from dataclasses import dataclass
 
+from paddle_billing.Operation import Operation
 from paddle_billing.Undefined import Undefined
 from paddle_billing.Entities.Shared import (
-    BillingDetails,
     Checkout,
     CollectionMode,
     CurrencyCode,
@@ -11,10 +11,11 @@
     TransactionStatus,
 )
 from paddle_billing.Entities.Transactions import TransactionCreateItem, TransactionCreateItemWithPrice
+from paddle_billing.Resources.Transactions.Operations.Update import UpdateBillingDetails
 
 
 @dataclass
-class UpdateTransaction:
+class UpdateTransaction(Operation):
     items: list[TransactionCreateItem | TransactionCreateItemWithPrice] = Undefined()
     status: TransactionStatus | Undefined = Undefined()
     customer_id: str | None | Undefined = Undefined()
@@ -24,9 +25,6 @@ class UpdateTransaction:
     currency_code: CurrencyCode | Undefined = Undefined()
     collection_mode: CollectionMode | Undefined = Undefined()
     discount_id: str | None | Undefined = Undefined()
-    billing_details: BillingDetails | None | Undefined = Undefined()
+    billing_details: UpdateBillingDetails | None | Undefined = Undefined()
     billing_period: TimePeriod | None | Undefined = Undefined()
     checkout: Checkout | None | Undefined = Undefined()
-
-    def get_parameters(self) -> dict:
-        return asdict(self)
diff --git a/paddle_billing/Resources/Transactions/TransactionsClient.py b/paddle_billing/Resources/Transactions/TransactionsClient.py
index 7d792ad9..7af36612 100644
--- a/paddle_billing/Resources/Transactions/TransactionsClient.py
+++ b/paddle_billing/Resources/Transactions/TransactionsClient.py
@@ -67,13 +67,13 @@ def create(self, operation: CreateTransaction, includes=None) -> Transaction:
             )
 
         params = {"include": ",".join(include.value for include in includes)} if includes else {}
-        self.response = self.client.post_raw("/transactions", operation.get_parameters(), params)
+        self.response = self.client.post_raw("/transactions", operation, params)
         parser = ResponseParser(self.response)
 
         return Transaction.from_dict(parser.get_data())
 
     def update(self, transaction_id: str, operation: UpdateTransaction) -> Transaction:
-        self.response = self.client.patch_raw(f"/transactions/{transaction_id}", operation.get_parameters())
+        self.response = self.client.patch_raw(f"/transactions/{transaction_id}", operation)
         parser = ResponseParser(self.response)
 
         return Transaction.from_dict(parser.get_data())
diff --git a/tests/Functional/Resources/Subscriptions/_fixtures/request/preview_update_full_billing_details.json b/tests/Functional/Resources/Subscriptions/_fixtures/request/preview_update_full_billing_details.json
new file mode 100644
index 00000000..e310fdef
--- /dev/null
+++ b/tests/Functional/Resources/Subscriptions/_fixtures/request/preview_update_full_billing_details.json
@@ -0,0 +1,11 @@
+{
+  "billing_details": {
+    "additional_information": "Some additional information",
+    "enable_checkout": true,
+    "purchase_order_number": "10009",
+    "payment_terms": {
+      "interval": "month",
+      "frequency": 1
+    }
+  }
+}
diff --git a/tests/Functional/Resources/Subscriptions/_fixtures/request/preview_update_minimal_billing_details.json b/tests/Functional/Resources/Subscriptions/_fixtures/request/preview_update_minimal_billing_details.json
new file mode 100644
index 00000000..d3cc90c5
--- /dev/null
+++ b/tests/Functional/Resources/Subscriptions/_fixtures/request/preview_update_minimal_billing_details.json
@@ -0,0 +1,3 @@
+{
+  "billing_details": {}
+}
diff --git a/tests/Functional/Resources/Subscriptions/_fixtures/request/update_full_billing_details.json b/tests/Functional/Resources/Subscriptions/_fixtures/request/update_full_billing_details.json
new file mode 100644
index 00000000..e310fdef
--- /dev/null
+++ b/tests/Functional/Resources/Subscriptions/_fixtures/request/update_full_billing_details.json
@@ -0,0 +1,11 @@
+{
+  "billing_details": {
+    "additional_information": "Some additional information",
+    "enable_checkout": true,
+    "purchase_order_number": "10009",
+    "payment_terms": {
+      "interval": "month",
+      "frequency": 1
+    }
+  }
+}
diff --git a/tests/Functional/Resources/Subscriptions/_fixtures/request/update_minimal_billing_details.json b/tests/Functional/Resources/Subscriptions/_fixtures/request/update_minimal_billing_details.json
new file mode 100644
index 00000000..d3cc90c5
--- /dev/null
+++ b/tests/Functional/Resources/Subscriptions/_fixtures/request/update_minimal_billing_details.json
@@ -0,0 +1,3 @@
+{
+  "billing_details": {}
+}
diff --git a/tests/Functional/Resources/Subscriptions/test_SubscriptionsClient.py b/tests/Functional/Resources/Subscriptions/test_SubscriptionsClient.py
index 216526c6..892032a6 100644
--- a/tests/Functional/Resources/Subscriptions/test_SubscriptionsClient.py
+++ b/tests/Functional/Resources/Subscriptions/test_SubscriptionsClient.py
@@ -52,6 +52,8 @@
     UpdateSubscription,
 )
 
+from paddle_billing.Resources.Subscriptions.Operations.Update import UpdateBillingDetails
+
 from tests.Utils.ReadsFixture import ReadsFixtures
 
 
@@ -142,11 +144,36 @@ class TestSubscriptionsClient:
                 ReadsFixtures.read_raw_json_fixture("response/full_entity"),
                 "/subscriptions/sub_01h8bx8fmywym11t6swgzba704",
             ),
+            (
+                "sub_01h8bx8fmywym11t6swgzba704",
+                UpdateSubscription(billing_details=UpdateBillingDetails()),
+                ReadsFixtures.read_raw_json_fixture("request/update_minimal_billing_details"),
+                200,
+                ReadsFixtures.read_raw_json_fixture("response/full_entity"),
+                "/subscriptions/sub_01h8bx8fmywym11t6swgzba704",
+            ),
+            (
+                "sub_01h8bx8fmywym11t6swgzba704",
+                UpdateSubscription(
+                    billing_details=UpdateBillingDetails(
+                        enable_checkout=True,
+                        payment_terms=Duration(interval=Interval.Month, frequency=1),
+                        purchase_order_number="10009",
+                        additional_information="Some additional information",
+                    ),
+                ),
+                ReadsFixtures.read_raw_json_fixture("request/update_full_billing_details"),
+                200,
+                ReadsFixtures.read_raw_json_fixture("response/full_entity"),
+                "/subscriptions/sub_01h8bx8fmywym11t6swgzba704",
+            ),
         ],
         ids=[
             "Update subscription with a single new value",
             "Update subscription with partial new values",
             "Update subscription with all new values",
+            "Update subscription with minimal billing details",
+            "Update subscription with full billing details",
         ],
     )
     def test_update_subscription_uses_expected_payload(
@@ -902,11 +929,38 @@ def test_create_subscription_one_time_charge_uses_expected_payload(
                 ReadsFixtures.read_raw_json_fixture("response/preview_update_full_entity"),
                 "/subscriptions/sub_01h8bx8fmywym11t6swgzba704/preview",
             ),
+            (
+                "sub_01h8bx8fmywym11t6swgzba704",
+                PreviewUpdateSubscription(
+                    billing_details=UpdateBillingDetails(),
+                ),
+                ReadsFixtures.read_raw_json_fixture("request/preview_update_minimal_billing_details"),
+                200,
+                ReadsFixtures.read_raw_json_fixture("response/preview_update_full_entity"),
+                "/subscriptions/sub_01h8bx8fmywym11t6swgzba704/preview",
+            ),
+            (
+                "sub_01h8bx8fmywym11t6swgzba704",
+                PreviewUpdateSubscription(
+                    billing_details=UpdateBillingDetails(
+                        enable_checkout=True,
+                        payment_terms=Duration(interval=Interval.Month, frequency=1),
+                        purchase_order_number="10009",
+                        additional_information="Some additional information",
+                    ),
+                ),
+                ReadsFixtures.read_raw_json_fixture("request/preview_update_full_billing_details"),
+                200,
+                ReadsFixtures.read_raw_json_fixture("response/preview_update_full_entity"),
+                "/subscriptions/sub_01h8bx8fmywym11t6swgzba704/preview",
+            ),
         ],
         ids=[
             "Preview updating a subscription with a single new value",
             "Preview updating a subscription with partial new values",
             "Preview updating a subscription with all new values",
+            "Preview updating a subscription with minimal billing details",
+            "Preview updating a subscription with full billing details",
         ],
     )
     def test_preview_update_subscription_uses_expected_payload(
diff --git a/tests/Functional/Resources/Transactions/_fixtures/request/create_full_billing_details.json b/tests/Functional/Resources/Transactions/_fixtures/request/create_full_billing_details.json
new file mode 100644
index 00000000..5262ec59
--- /dev/null
+++ b/tests/Functional/Resources/Transactions/_fixtures/request/create_full_billing_details.json
@@ -0,0 +1,17 @@
+{
+  "items": [
+    {
+      "quantity": 1,
+      "price_id": "pri_01gsz8x8sawmvhz1pv30nge1ke"
+    }
+  ],
+  "billing_details": {
+    "additional_information": "Some additional information",
+    "enable_checkout": true,
+    "purchase_order_number": "10009",
+    "payment_terms": {
+      "interval": "month",
+      "frequency": 1
+    }
+  }
+}
diff --git a/tests/Functional/Resources/Transactions/_fixtures/request/create_manual.json b/tests/Functional/Resources/Transactions/_fixtures/request/create_manual.json
index 40b4d5fe..47f3180f 100644
--- a/tests/Functional/Resources/Transactions/_fixtures/request/create_manual.json
+++ b/tests/Functional/Resources/Transactions/_fixtures/request/create_manual.json
@@ -13,7 +13,6 @@
   "collection_mode": "manual",
   "discount_id": "dsc_01hen7bjzh12m0v2peer15d9qt",
   "billing_details": {
-    "additional_information": null,
     "enable_checkout": true,
     "purchase_order_number": "10009",
     "payment_terms": {
diff --git a/tests/Functional/Resources/Transactions/_fixtures/request/create_minimal_billing_details.json b/tests/Functional/Resources/Transactions/_fixtures/request/create_minimal_billing_details.json
new file mode 100644
index 00000000..3570093d
--- /dev/null
+++ b/tests/Functional/Resources/Transactions/_fixtures/request/create_minimal_billing_details.json
@@ -0,0 +1,14 @@
+{
+  "items": [
+    {
+      "quantity": 1,
+      "price_id": "pri_01gsz8x8sawmvhz1pv30nge1ke"
+    }
+  ],
+  "billing_details": {
+    "payment_terms": {
+      "interval": "month",
+      "frequency": 1
+    }
+  }
+}
diff --git a/tests/Functional/Resources/Transactions/_fixtures/request/update_full_billing_details.json b/tests/Functional/Resources/Transactions/_fixtures/request/update_full_billing_details.json
new file mode 100644
index 00000000..e310fdef
--- /dev/null
+++ b/tests/Functional/Resources/Transactions/_fixtures/request/update_full_billing_details.json
@@ -0,0 +1,11 @@
+{
+  "billing_details": {
+    "additional_information": "Some additional information",
+    "enable_checkout": true,
+    "purchase_order_number": "10009",
+    "payment_terms": {
+      "interval": "month",
+      "frequency": 1
+    }
+  }
+}
diff --git a/tests/Functional/Resources/Transactions/_fixtures/request/update_minimal_billing_details.json b/tests/Functional/Resources/Transactions/_fixtures/request/update_minimal_billing_details.json
new file mode 100644
index 00000000..66d67358
--- /dev/null
+++ b/tests/Functional/Resources/Transactions/_fixtures/request/update_minimal_billing_details.json
@@ -0,0 +1,8 @@
+{
+  "billing_details": {
+    "payment_terms": {
+      "interval": "month",
+      "frequency": 1
+    }
+  }
+}
diff --git a/tests/Functional/Resources/Transactions/test_TransactionsClient.py b/tests/Functional/Resources/Transactions/test_TransactionsClient.py
index fb6de294..ae4f9c02 100644
--- a/tests/Functional/Resources/Transactions/test_TransactionsClient.py
+++ b/tests/Functional/Resources/Transactions/test_TransactionsClient.py
@@ -12,7 +12,6 @@
 
 from paddle_billing.Entities.Shared import (
     AddressPreview,
-    BillingDetails,
     CollectionMode,
     CountryCode,
     CurrencyCode,
@@ -50,6 +49,9 @@
     GetTransactionInvoice,
 )
 
+from paddle_billing.Resources.Transactions.Operations.Create import CreateBillingDetails
+from paddle_billing.Resources.Transactions.Operations.Update import UpdateBillingDetails
+
 from tests.Utils.ReadsFixture import ReadsFixtures
 
 
@@ -156,7 +158,7 @@ def test_list_transaction_can_paginate(self, test_client, mock_requests, operati
                     currency_code=CurrencyCode.GBP,
                     collection_mode=CollectionMode.Manual,
                     discount_id="dsc_01hen7bjzh12m0v2peer15d9qt",
-                    billing_details=BillingDetails(
+                    billing_details=CreateBillingDetails(
                         enable_checkout=True,
                         payment_terms=Duration(interval=Interval.Month, frequency=1),
                         purchase_order_number="10009",
@@ -167,11 +169,40 @@ def test_list_transaction_can_paginate(self, test_client, mock_requests, operati
                 ReadsFixtures.read_raw_json_fixture("response/full_entity"),
                 "/transactions",
             ),
+            (
+                CreateTransaction(
+                    items=[TransactionCreateItem(price_id="pri_01gsz8x8sawmvhz1pv30nge1ke", quantity=1)],
+                    billing_details=CreateBillingDetails(
+                        payment_terms=Duration(interval=Interval.Month, frequency=1),
+                    ),
+                ),
+                ReadsFixtures.read_raw_json_fixture("request/create_minimal_billing_details"),
+                200,
+                ReadsFixtures.read_raw_json_fixture("response/full_entity"),
+                "/transactions",
+            ),
+            (
+                CreateTransaction(
+                    items=[TransactionCreateItem(price_id="pri_01gsz8x8sawmvhz1pv30nge1ke", quantity=1)],
+                    billing_details=CreateBillingDetails(
+                        enable_checkout=True,
+                        payment_terms=Duration(interval=Interval.Month, frequency=1),
+                        purchase_order_number="10009",
+                        additional_information="Some additional information",
+                    ),
+                ),
+                ReadsFixtures.read_raw_json_fixture("request/create_full_billing_details"),
+                200,
+                ReadsFixtures.read_raw_json_fixture("response/full_entity"),
+                "/transactions",
+            ),
         ],
         ids=[
             "Create transaction with basic data",
             "Create transaction with non-catalog price",
             "Create transaction with manual collection mode",
+            "Create transaction with minimal billing details",
+            "Create transaction with full billing details",
         ],
     )
     def test_create_transaction_uses_expected_payload(
@@ -266,10 +297,39 @@ def test_create_transaction_with_includes_returns_expected_payload(
                 ReadsFixtures.read_raw_json_fixture("response/full_entity"),
                 "/transactions/txn_01h7zcgmdc6tmwtjehp3sh7azf",
             ),
+            (
+                "txn_01h7zcgmdc6tmwtjehp3sh7azf",
+                UpdateTransaction(
+                    billing_details=UpdateBillingDetails(
+                        payment_terms=Duration(interval=Interval.Month, frequency=1),
+                    ),
+                ),
+                ReadsFixtures.read_raw_json_fixture("request/update_minimal_billing_details"),
+                200,
+                ReadsFixtures.read_raw_json_fixture("response/full_entity"),
+                "/transactions/txn_01h7zcgmdc6tmwtjehp3sh7azf",
+            ),
+            (
+                "txn_01h7zcgmdc6tmwtjehp3sh7azf",
+                UpdateTransaction(
+                    billing_details=UpdateBillingDetails(
+                        enable_checkout=True,
+                        payment_terms=Duration(interval=Interval.Month, frequency=1),
+                        purchase_order_number="10009",
+                        additional_information="Some additional information",
+                    ),
+                ),
+                ReadsFixtures.read_raw_json_fixture("request/update_full_billing_details"),
+                200,
+                ReadsFixtures.read_raw_json_fixture("response/full_entity"),
+                "/transactions/txn_01h7zcgmdc6tmwtjehp3sh7azf",
+            ),
         ],
         ids=[
             "Update transaction with single new value",
             "Update transaction with partial new values",
+            "Create transaction with minimal billing details",
+            "Create transaction with full billing details",
         ],
     )
     def test_update_transaction_uses_expected_payload(