Domain is set up but not showing up as a Branded Domain

I have verified that a domain is set up appropriately but it is not yet showing up as a branded domain that we can use in an invitation that we're getting ready to send out.    I'm thinking I'm missing a step that would add that to the list of domains to choose from.   Can someone point me in the right direction on what I need to do to make that domain available within the email set up?