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?
Admin > Email > Branded domain
you need to add it after the CNAME is setup on your DNS.
If it still doesn't work, ask Support. Recently had a misconfiguration on that due to HTTPS issue.