Error: We can't create your email address until you verify that you own this domain
You'll see this error message in your Office 365 from GoDaddy account if you're trying to use an external domain for your email address. This is any domain at another domain provider, or in another account. Even if it's another GoDaddy domain, if it's in a different GoDaddy account, it's still considered external.
Verify your ownership of the domain in order to proceed with your Office 365 setup.