Hello Charles,
once again an example from our PayPal Plugin We extended the confirm form, to send additional data if the customer submits the order: SwagPayPal/index.html.twig at master · shopwareLabs/SwagPayPal · GitHub
This values are now available in the PaymentHandler, e.g: https://github.com/shopwareLabs/SwagPayPal/blob/master/src/Payment/PayPalPaymentHandler.php#L96
I don’t see why you would need an own controller Hope this helps
Best regards from Schöppingen
Michael Telgmann