Bookings Sending Domain

Trying to work through a problem that when we send Bookings appointments to outside or domain, it never sends. It is primarily due to our onmicrosoft.com domain is not actually set up and we do everything through our primary domain. 

I see that you can set the "BookingsMailboxDomain" through Set-OwaMailboxPolicy. Which I created a new mailboxpolicy and set that to the correct domain. However, when I run a get-casmailbox it won't find the user, I assume since it is a scheduling mailbox type? So I cannot assign the mailbox policy to it. Even if I assign it an exchange license.

Any other ideas out there?