Greetings and welcome to the Community!
How is the default domain configured within the Office 365 admin portal? It's important to set the default domain to <company>.onmicrosoft.com and not your actual production domain. Also make sure your Office 365 admin account has Global Administrator permissions.
Take a look at our Office 365 checklist and double-check your setup. If still having issues with the domains, let us know.
Thanks,
-Tony