Can't switch to new phones (same brand, just newer models)

xfinity mobile (phone app or website) > upgrade or switch devices > check compatibility > Enter IMEI > "Something went wrong, please try again". Tied 6 times between the phone app and the website. Never works.

I want to update the Xfinity mobile system to the newer Devices and their new IMEI numbers. The phones have been using the Xfinity network for about 5 days now (I moved the SIMs to the new phones), compatibility was checked before we bought the new unlocked phones, all looks good except for the information stored by Xfinity Mobile.

Does Xfinity not need to know about this change?