diff --git a/src/lumina/database/models.py b/src/lumina/database/models.py
index df0eb49..9934b18 100644
--- a/src/lumina/database/models.py
+++ b/src/lumina/database/models.py
@@ -14,7 +14,7 @@ class DynamoExportMixin:
     def ddict(self: BaseModelProtocol, **kwargs):
         """dict() export for DynamoDB, removes any Python-only fields, essentially
         JSON but still in dict form"""
-        return jsonable_encoder(self.dict(**kwargs))
+        return jsonable_encoder(self.model_dump(**kwargs))
 
 
 class BaseDynamoModel(BaseModel):
@@ -96,5 +96,7 @@ class SubmissionModel(BaseDynamoModel, DynamoExportMixin):
 
     @property
     def issue_id(self) -> int:
-        # TODO: Use this when we have Python 3.9
-        return int(self.sk.split("/")[-1])
+        try:
+            return int(self.sk.removeprefix(table.SK_SUBMISSION_PREFIX))
+        except ValueError as e:
+            raise ValueError(f"Invalid target_id: {self.sk}, cannot parse int") from e
diff --git a/src/lumina/database/operations.py b/src/lumina/database/operations.py
index fb3e719..5ea555c 100644
--- a/src/lumina/database/operations.py
+++ b/src/lumina/database/operations.py
@@ -131,7 +131,7 @@ def move_anonymous_submissions_to_member(
         # Create a new submission using the member ID
         new_member_submissions.append(
             # Direct copy and change only the PK
-            put_submission(anonymous_submission.copy(update={"pk": member_id}))
+            put_submission(anonymous_submission.model_copy(update={"pk": member_id}))
         )
         # Delete the old submission
         delete_response = get_member_table().delete_item(
diff --git a/src/lumina/github/webhooks.py b/src/lumina/github/webhooks.py
index 5df0b8a..45a422c 100644
--- a/src/lumina/github/webhooks.py
+++ b/src/lumina/github/webhooks.py
@@ -46,7 +46,7 @@ def verify_webhook(signature: str, body: bytes) -> bool:
 
 
 def update_issue_from_webhook(webhook: GitHubWebhook) -> None:
-    github_issue = GitHubIssueModel(**webhook.issue.dict())
+    github_issue = GitHubIssueModel(**webhook.issue.model_dump())
     github_issue.state = get_state_from_issue(webhook.issue)
     if not webhook.issue:
         raise ValueError("Webhook does not contain an issue")
diff --git a/tests/unit/lumina/database/test_operations.py b/tests/unit/lumina/database/test_operations.py
index 5a47e2b..ec96809 100644
--- a/tests/unit/lumina/database/test_operations.py
+++ b/tests/unit/lumina/database/test_operations.py
@@ -109,7 +109,7 @@ def _make_submission(id: int, **kwargs) -> SubmissionModel:
             closed_at=None,
             comments=0,
         ),
-    ).copy(update=kwargs)
+    ).model_copy(update=kwargs)
 
 
 def test_put_member_submission():
@@ -189,7 +189,7 @@ def test_update_submission_github_issue():
     to_close_at = dates.now()
     operations.update_submission_github_issue(
         101,
-        new_submission.github_issue.copy(
+        new_submission.github_issue.model_copy(
             update={
                 "state": GitHubIssueState.CLOSED,
                 "comments": 5,
diff --git a/tests/unit/lumina/endpoints/test_member.py b/tests/unit/lumina/endpoints/test_member.py
index 198c415..6bb4d74 100644
--- a/tests/unit/lumina/endpoints/test_member.py
+++ b/tests/unit/lumina/endpoints/test_member.py
@@ -77,7 +77,7 @@ def test_success_self_first_call(
         auth_fred_bloggs,
         snapshot,
     ):
-        mock_get_member.return_value = MemberModel(**auth_fred_bloggs.dict())
+        mock_get_member.return_value = MemberModel(**auth_fred_bloggs.model_dump())
         mock_get_member.return_value.email_verified_at = "2021-01-01T00:00:00"
         response = client.get("/member/fred_bloggs")
         assert response.status_code == HTTPStatus.OK, response.json()
diff --git a/tests/unit/lumina/endpoints/test_submissions.py b/tests/unit/lumina/endpoints/test_submissions.py
index 2443a89..1616308 100644
--- a/tests/unit/lumina/endpoints/test_submissions.py
+++ b/tests/unit/lumina/endpoints/test_submissions.py
@@ -252,9 +252,9 @@ def test_success_not_authed(self):
                 # This mess needed as pydantic doesn't serialise UUID by default
                 # See https://github.com/samuelcolvin/pydantic/issues/1157
                 json={
-                    **submission_request.dict(),
+                    **submission_request.model_dump(),
                     "submitter": {
-                        **submission_request.submitter.dict(),
+                        **submission_request.submitter.model_dump(),
                         "id": str(submission_request.submitter.id),
                     },
                 },
@@ -311,7 +311,7 @@ def test_success_authed(self, auth_fred_bloggs):
             )
             response = client.post(
                 "/submissions/message",
-                json=submission_request.dict(),
+                json=submission_request.model_dump(),
             )
         assert response.status_code == HTTPStatus.OK
         assert response.json() == {
diff --git a/tests/unit/lumina/github/test_webhooks.py b/tests/unit/lumina/github/test_webhooks.py
index 416b5eb..4410698 100644
--- a/tests/unit/lumina/github/test_webhooks.py
+++ b/tests/unit/lumina/github/test_webhooks.py
@@ -87,7 +87,7 @@ def test_issue_closed(self):
             webhooks.handle_webhook(ISSUE_CLOSED_HOOK)
         assert mock_update_issue.call_count == 1
         assert mock_update_issue.call_args[0][1] == GitHubIssueModel(
-            **ISSUE_CLOSED_HOOK.issue.dict()
+            **ISSUE_CLOSED_HOOK.issue.model_dump()
         )
 
     def test_issue_completed(self):