Originally Posted by
tmiw
When I was using an iPhone I found that going to the Wallet app and pre-authenticating before tapping made the transaction run more quickly than waiting for the phone to detect the NFC field first. I'm not sure if this is still true though, especially since I was using a 6s before.
Double-press the sleep/wake button and authenticate with Face ID or double-press the home button and authenticate with Touch ID (one combined step), then hold it near the terminal to pay. Optionally, switch cards before paying.
There's no need to wait for the phone to detect NFC or to unlock it to launch the Wallet app or any other app, although that does work.