Additional features, settings, or issues not covered by specific Microsoft Teams categories
For anyone else that finds this thread, I had the same issue. Licenses were assigned properly, Phone number was assigned to the account in the Teams Admin Centre, but I still got this issue. I found that i could dial out but not dial in. It turns out that my DNS settings were not correct. In my case, we did not have SRV records set up for siptls or _sipfederationtls_tcp. Once we added those, all worked as expected.