How do I replace double side click with assistive touch?

When you go to settings>accessibility>touch>assistive touch>scroll down to the bottom of the screen - do you have something called "confirm with assistive touch?" That may be your alternate solution.

Hey Stellina2,

We see that you want to change how you use Apple Pay using AssistiveTouch, and we'd like to help!

Here's a helpful user guide for AssistiveTouch that you can check out: Use AssistiveTouch on iPhone

If you don't see the feature that you want from the guide, we suggest that you leave a valuable feedback to Apple here: Product Feedback

We hope this helps!

Best regards.

You are stuck with double clicking then. I do not know of any other options besides turning on Face ID. I believe you can set Face ID just for Apple Pay and turn everything else off.

Have you tried hold the device near the pay terminal when you are ready to pay? That should bring up Face ID or Touch ID