The NFC chip (which facilitates Apple Pay) is located on the back of the display so swapping out the display can cause the encrypted information associated with Apple Pay to be lost. It's connected to the logic board from there (just like touch ID on older iPhones). [link|https://www.reddit.com/r/mobilerepair/comments/jyroh2/comment/grwmkxu/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button|Check this reddit post|new_window=true]
Also check this [post|461445|answers from iFixit about NFC on series 2|new_window=true].
Hope this help you!