In the next step, you'll add all the domains that you're using with your local directory to Office 365. We also need you ...

In the next step, you'll add all the domains that you're using with your local directory to Office 365. We also need you to add a TXT record to DNS to show us that you're the registered domain owner before you start to sync.  Non-routable domains aren't supported, so you may need to add an alternate UPN suffix in Active Directory.