"Sorry we are unable to process your request. You need to pay in full" Error

Getting the above error when trying to trade in my current Iphone 11 for a Iphone 16 on the xfinity website.  Iphone 11 is in perfect condition, still in use every day.  Has had a strong case for the entire time I have owned it, no damage at all.   Getting the error message when I enter in the IMEI and try to add the new phone to my cart.  Already been frustrated with Xfinity mobile, if I can not get this resolved I am finally just going to move to a new carrier.  Why promise trade in credits if you don't want to give them out?  Just dishonest behavior.