Apple Pay, "Hold near reader", what should I replace?

Hi there, just recently I had run into issues with Apple Pay on my first gen SE where it’s no longer recognizing terminals and saying "Hold near reader”. I suspect it’s a hardware issue just due to the fact on how it stopped working. I’ve read some posts already on this site but am unclear on what I should get repaired.

I had my power button replaced due to that being damaged so maybe check the flex cable? Can that be replaced?

Would the NFC chip need replaced? CAN it be replaced? Actually, can it be upgraded too? :o

thanks!