Interesting -- I spent literally 2 hours today at the Apple Store doing the exact same thing.. Both the associate as well as the store manager had issues doing it at every step. Finally, instead of trying to do the trade in against the previous phone's serial number, they did it against my order number for the 13 Pro. I'm still not entirely sure if they did it correctly because they had me activate Apple Pay on my phone to issue the credit and I was able to choose what card they credited back to from my iOS Wallet. The other thing I'm concerned about is the manager said because it was originally set up as an online trade-in and not in-store, that the trade would de-couple from my original order, and any carrier promo I may have been eligible for would be canceled because of that. In my case, I was taking advantage of the T-Mobile $200 in bill credits for doing the trade in addition to Apple's trade-in credit. I paid in full for the phone.
I did get a "Drop off confirmation" receipt showing the credit to my Apple Pay Device card number for the card I selected (which was the same card I purchased originally with)
