The domain from Microsoft Office you want to use, when setting up Direct Routing in the Enterprise portal, is failing
The domain is not ‘healthy’ in Microsoft Office >> Admin Settings >> Domains. Go into Office Admin and follow the process to bring the domain into a healthy state.
The domain you select needs to be enabled for a Service called “Skype”. You can confirm this by looking at the Microsoft Adminb >>Domains screen and exposing the additional column called Services as below
If Skype services are not enabled on your chosen domain then you must add it manually on the “Manage DNS” screen.