How to change Apple Pay from passcode to Touch ID?

If you have a compatible device, go to Settings ➜ Touch ID & Passcode ➜ [Use Touch ID For] Wallet & Apple Pay and make sure it's turned on.

Use Touch ID on iPhone and iPad - Apple Support

An iPhone 13 Pro Max as shown on your device line, cannot use Touch ID (it lacks the fingerprint sensor), but can use Face ID instead for Wallet & Apple Pay.

The double click is always required to avoid unintended purchases. After the double click if the option in Settings ➜ Face ID & Passcode ➜ [Use Face ID For] Wallet & Apple Pay is turned on, it will verify you through Face ID as soon as you double click the button.

The Face ID icon should appear on screen just after you double click the sleep button.

click here ➜ Use Face ID on your iPhone or iPad Pro - Apple Support

Some payments such as mass transit work like that yes.

For other purchases, you must authenticate first and then hold the device up to the terminal to complete the purchase.

Are you having difficulty doing the double click, is that the issue? Double click speed etc. can be adjusted in Accessibility.

I’m 67 and I’m starting to notice a little stiffness in my fingers and realize I’m not quite as fast as I used to be. Combined with the Face ID, that might well be the ticket.