Hey there, MizzAJ.
Welcome to the Apple Support Communities! Thanks for posting about AssistiveTouch when confirming payments when using Face ID. We'd be glad to help.
The feature you're seeing is optional, so if you'd prefer to tap the side button for confirmation rather than use AssistiveTouch, go to Settings > Accessibility > Touch > AssistiveTouch > Confirm with AssistiveTouch and turn it off there. To learn more about AssistiveTouch in general, read over Use AssistiveTouch on your iPhone, iPad, or iPod touch.
If you have any other questions, be sure to let us know.
Take care.