Apple Pay works but phone won’t scan an NFC (freestyle libre - medical device)

I use my phone as a medical device to check my blood sugars (diabetes) - the Freestyle libre device uses NFC - I scan it and it tells me my blood sugars.

I’ve used my phone (iPhone SE) for this for over a year with no ottomans but the other day it suddenly just won’t scan. The sensors work as I’ve used a separate reader to check them. I’ve restarted my phone, deleted and reinstalled the app, cleared the data and even fully wiped and rebooted my phone and it still doesn’t work.

if the NFC is broken (I’ve tried it in something else too and it doesn’t read) why does apple pay still work in the shops???