@Matt_Yu_Zhang Thank you for reaching out to Microsoft Q&A, apologize for any inconvenience caused with this.
I have also tried to create a message endpoint using the shared ARM template, we are also landed up with the same issue.
Post the reviewing the deploying logs we see that deployment got failed while deploying the github source code to app service it is failing with error.
Build FAILED.
"C:\home\site\repository\viewer\viewer.csproj" (Restore target) (1) ->
"C:\home\site\repository\viewer\viewer.csproj" (_GenerateRestoreGraphProjectEntry target) (1:5) ->
(_CheckForUnsupportedNETCoreVersion target) ->
C:\Program Files (x86)\dotnet\sdk\2.2.109\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.TargetFrameworkInference.targets(137,5): error NETSDK1045: The current .NET SDK does not support targeting .NET Core 3.1. Either target .NET Core 2.2 or lower, or use a version of the .NET SDK that supports .NET Core 3.1. [C:\home\site\repository\viewer\viewer.csproj]
0 Warning(s)
1 Error(s)
As a workaround, we have pulled the source code to our local machine and tried building, publishing the source code from local visual studio to provisioned app service and able to request the endpoint without any issues.
I have relayed the same feedback to content author they will be reviewing and updating the documentation accordingly.
Hope this helps! Let me know if you have any further questions on this.