This how Apple Pay works to make a physical payment (which is the main case of this thread):
1 - Click two times on the iPhone powerbutton
2 - Unlock the phone with the FaceID
3 - Take the phone and put it on top of the terminal
ALSO, if you're already using your phone, you must press again the powerbutton two times, unlock Apple Pay with FaceID and then put the phone on top of the terminal.
Google Pay (using a Galaxy S22...)
1 - Unlock the phone using the fingerprint reader
2 - Put it on top of the terminal
If you're already using the phone just put it on top of a terminal and will pay your bill.
Seems like a small issue, but considering that until a few weeks ago we were still using masks, I sometimes had to input my phone pin in front of everyone to access Apple Pay, even if I had the phone unlocked before getting to the pay terminal...