Add warnings/alerts about the breaking change related to BSUID

Author: glorialimicrosoft

articles/communication-services/concepts/advanced-messaging/whatsapp/whatsapp-overview.md

@@ -33,8 +33,8 @@ The key features of Azure Communications Services Advanced Messaging for WhatsAp
 
 WhatsApp is launching usernames in 2026, allowing users to display a username instead of their phone number. To support this change, Meta introduces a new identifier called the **business-scoped user ID (BSUID)**. BSUIDs begin appearing in webhook payloads and can be used as recipient identifiers in send requests.
 
-> [!IMPORTANT]
-> The `from` and `to` fields in Advanced Messaging events may now be empty when a user hides their phone number. Update your event handlers to use the new `fromBSUID` and `toBSUID` fields. For more information, see [WhatsApp usernames and BSUIDs](./whatsapp-usernames-business-scoped-user-identifier.md).
+> [!WARNING]
+> **Breaking change:** The `from` and `to` fields in Advanced Messaging events may now be empty when a user hides their phone number. Update your event handlers to use the new `fromBSUID` and `toBSUID` fields. For more information, see [WhatsApp usernames and BSUIDs](./whatsapp-usernames-business-scoped-user-identifier.md).
 
 ## Next steps
 

articles/communication-services/concepts/advanced-messaging/whatsapp/whatsapp-usernames-business-scoped-user-identifier.md

@@ -151,6 +151,9 @@ Meta provides a Contact Book feature that automatically stores WhatsApp user con
 
 ## How to prepare
 
+> [!WARNING]
+> **Breaking change:** The `from` and `to` fields in Advanced Messaging events may now be empty or null. Any code that assumes these fields always contain a phone number will break. You must update your event handlers to use the new `fromBSUID` and `toBSUID` fields.
+
 To prepare your integration for WhatsApp usernames and BSUIDs:
 
 1. **Stop assuming `from` and `to` always contain phone numbers.** Review any logic that parses, validates, or formats these fields as E.164 numbers. These fields may now be empty or null.

articles/communication-services/quickstarts/advanced-messaging/whatsapp/handle-advanced-messaging-events.md

@@ -96,8 +96,8 @@ With the introduction of WhatsApp usernames, Advanced Messaging events now inclu
 - **`AdvancedMessageReceived`** events include a `fromBSUID` field with the sender's BSUID.
 - **`AdvancedMessageDeliveryStatusUpdated`** events include a `toBSUID` field with the recipient's BSUID.
 
-> [!IMPORTANT]
-> The existing `from` and `to` fields may now be empty or null when a WhatsApp user has adopted a username and hidden their phone number. Update your event handlers accordingly. For more information, see [WhatsApp usernames and BSUIDs](../../../concepts/advanced-messaging/whatsapp/whatsapp-usernames-business-scoped-user-identifier.md).
+> [!WARNING]
+> **Breaking change:** The existing `from` and `to` fields may now be empty or null when a WhatsApp user has adopted a username and hidden their phone number. Update your event handlers accordingly. For more information, see [WhatsApp usernames and BSUIDs](../../../concepts/advanced-messaging/whatsapp/whatsapp-usernames-business-scoped-user-identifier.md).
 
 ## Next steps
 

articles/event-grid/communication-services-advanced-messaging-events.md

@@ -36,6 +36,9 @@ Example scenario: A WhatsApp user sends a WhatsApp message to a WhatsApp Busines
 
 #### Attribute list
 
+> [!WARNING]
+> **Breaking change:** The `from` field may now be empty when a WhatsApp user has adopted a username and hidden their phone number. Update your event handlers to use the new `fromBSUID` field instead of relying solely on `from`. For more information, see [WhatsApp usernames and BSUIDs](/azure/communication-services/concepts/advanced-messaging/whatsapp/whatsapp-usernames-business-scoped-user-identifier).
+
 Details for the attributes specific to `Microsoft.Communication.AdvancedMessageReceived` events.
 
 | Attribute  | Type  | Nullable | Description |
@@ -347,6 +350,9 @@ Example scenario: Contoso uses an active Advanced Messaging channel connected to
 
 #### Attribute list
 
+> [!WARNING]
+> **Breaking change:** The `to` field may now be empty when the message was sent to a BSUID. Update your event handlers to use the new `toBSUID` field instead of relying solely on `to`. For more information, see [WhatsApp usernames and BSUIDs](/azure/communication-services/concepts/advanced-messaging/whatsapp/whatsapp-usernames-business-scoped-user-identifier).
+
 Details for the attributes specific to `Microsoft.Communication.AdvancedMessageReceived` events.
 
 | Attribute | Type | Nullable | Description |