What to do if I get the "hostname: example .onmicrosoft.com" is not valid" message?
This article explains steps that are needed to be taken in case if you are facing a "hostname: example .onmicrosoft.com" is not valid" error while creating a new tenant domain.
1. If you are not able to create a new tenant domain (see the image below), this means that this domain is already taken and exists in the Microsoft ecosystem.
To resolve this issue, please provide different Domain name.