Altinn Notification SMS mobile number specification (#1393)

* Altinn Notification SMS mobile number specification

* Review comment resolving

* Comments regarding country codes added

* Fixed typo and removed country code lists link

* Suggestion fra Stephanie

Co-authored-by: Stephanie Buadu <[email protected]>

* Fixed typos, grammer and made more clear the context

* Heading fixed

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Co-authored-by: Stephanie Buadu <[email protected]>

content/notifications/send-notifications/get-started/user-guide/_index.en.md

@@ -13,8 +13,18 @@ In the meantime existing guidelines for sending notifications through Altinn 2 a
 [Please familiarize yourself with existing documentation and guidelines](https://altinn.github.io/docs/utviklingsguider/varsling/)
 {{% /notice %}}
 
-
-
+## Notification
+### SMS
+- The mobile number must contain the country code, preferably with "+", while "00" would also work (e.g., +47900XXXXX, 0047900XXXXX).
+- SMS to 5-digit numbers is not supported.
+- Norwegian mobile numbers must start with "4" or "9" after the country code "+47."
+  - Valid Mobile Number Examples: +47400XXXXX, +47900XXXXX, 0047400XXXXX, 0047900XXXXX.
+  - Invalid Mobile Number Examples: +47500XXXXX, +47600XXXXX, 0047500XXXXX, 0047600XXXXX.
+
+#### International Mobile Number
+- We also support international mobile numbers (outside of Norway) to send SMS as long as they are valid and provided with a country code.
+- Notifications to 5-digit numbers aren't supported. Therefore, the mobile number must be more than 5 digits.
+- Country code in the mobile numbers undergo validation against a comprehensive list of country codes.
 
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 {{% notice info %}}