Apple Pay double click not working iPhone 13 Pro

Please follow this path,

iPhone > Settings > Accessibility > AssistiveTouch — disable, if it is disabled, momentarily enable and then disable again. 

Scroll down to bottom of AssistiveTouch screen > Confirm with AssistiveTouch > disable

After confirming above, please do a forced restart following the instructions in the Apple Support article linked below. If you’re unfamiliar with the procedure, follow the step by step instructions in the article. 

Force restart iPhone - Apple Support

Have you tried a full power-off and restart?

What’s it doing or not doing that makes you think it’s not working?

Also …

… did it indeed “work” previously and then “stop working” ????