Merge pull request #28647 from microsoftgraph/planner/pavlodatsiuk/taskchat-create-message-warning

Add known limitation note for creating planner task chat messages

Author: Danipocket

api-reference/beta/api/plannertask-post-messages.md

@@ -16,6 +16,9 @@ Namespace: microsoft.graph
 
 Create a new [plannerTaskChatMessage](../resources/plannertaskchatmessage.md) on a [plannerTask](../resources/plannertask.md).
 
+> [!IMPORTANT]
+> This method only supports creating a new chat message on a [plannerTask](../resources/plannertask.md) that already has at least one existing message.
+
 [!INCLUDE [national-cloud-support](../../includes/global-only.md)]
 
 ## Permissions