iPhone XS NFC Problems

Hi, I appreciate any help that I can get. I have recently refurbished an iPhone XS for a customer which included the back panel. Everything seemed to be fine until the customer got back to me saying that when paying at a supermarket they were not able to pay with Apple pay. To me, this sounds like an NFC problem however I don’t know how to fix this. Is it the wireless charging coil that has the NFC or is it on the motherboard? Never had this happen so a but bizarre.

Thanks