i am trying to setup auto attendant with on-premises telephone number.
I assigned on-premises number (not a service number) to a resources account and assign to auto attendant. I am getting a 404 response on SBC (reason No_USER_Responding), I enabled Teams only for the resource account but the issue is not resolved. also I enabled direct routing for the the number.
Did you assign a Phone System license to the resource account? If you did that you might have the same problem as I did when tested this, that there is something in the backend that Microsoft have to fix. I got the 404 error when the SBC tried to route calls to Teams, I created a support case with Microsoft and they "did a synchronization" in the system and it started to work.
I'm not sure it was the 404 issue; or another. But I had to open a premier case when these accounts weren't working correctly. The ticket came back from Microsoft that we had to explicitly set a DEPARTMENT on the AD Account "Microsoft Communication Application Instance"; (blew me away.....) the account would keep failing online in a get-csonlineuser with a InterpretedUserType of 'HybridOnlineAppEndpointFailedProvisioning'; For good measure I threw in first and last names and description on the account too. After a few hours of replication time it'd start working. So now on all accounts I build I put in a FirstName (givenNAme), LastName (surName), description, and department.