Hi You-Wish,
welcome to te Apple (user-to-user) Community!
Re: Apple Pay and AssistiveTouch: "use the Face ID to make purchases and to download apps,
on my iPad for pro". "Any ideas as to how to get it back"
Wondering if you might want to check if the correct settings are in place.
Apple support's online article for iOS 17 : Use AssistiveTouch on iPad - Apple Support
says you can:
Go to Settings > Accessibility > Touch > AssistiveTouch.
In the list of options: Tap: Confirm with AssistiveTouch:
On an iPad with Face ID, use AssistiveTouch to confirm payments with Face ID instead of
double-clicking the top button.
________________________________
If you still need help with this feature:
You may want to reach out to the Accessibility Support team:
See: How to contact Apple for accessibility support - Apple Support
or
Start from Apple's Accessibility Support Website
(NB: You can "Get Support" from the link at the bottom of their website:)
Accessibility Support - Official Apple Support
All the best :-)