To help debug donors being sent to incorrect payment forms, like the issue here, let's log the incoming $_SERVER['HTTP_REFERER'] and $_SERVER['REQUEST_URI'] or whatever the MediaWiki core equivalents are, in the payments-wiki logs. This will make life easier for us.
This will give us URLs like:
HTTP_REFERER => https://localhost:9001/index.php/Main_Page
REQUEST_URI => /index.php?title=Special:AdyenCheckoutGateway&appeal=JimmyQuote&payment_method=cc&recurring=0&uselang=en&language=en¤cy=USD&amount=10&country=US&first_name=Jimmy&last_name=Wales&street_address=1+Montgomery+Street&city=San+Francisco&state_province=CA&postal_code=94104&email=jwales%40example.com&debug=true