Effective September 1, 2019, your authorized user will need to wait at least 90 days before you can link their airline/hotel loyalty account to the primary Membership Rewards account. I believe this is American Express’s attempt to crack down on members selling their Membership Rewards Points by adding a buyer as an authorized user, then adding their airline/hotel loyalty account to the primary Membership Rewards account and then transferring Membership Rewards Points out of the primary account.
