Improve new Billing Request Flows to reduce failed attempts
The new billing request flows (currently in beta - see https://lab.civicrm.org/extensions/gocardless/-/releases/2.0.0beta1) introduces one of those annoying user experiences where the third party (GoCardless) site says something like "returning you to merchant in 3...2...1...<page-reload>`. Only when this reload happens is the processing done that sets up the subscription etc.
Users being users, we know statistically that some won't wait. Those users' subscriptions will never get setup. It will appear like they failed.
A fix for this would be to implement the billing_requests.fulfilled
webhook and have it do all the processing the thank you page does. The webhook would then be in a race with the 'return to merchant...' process as either could arrive first and we only want to process once. This is manageable though.
I'm listing this as an improvement to the new process. If enough funds come in to cover the costs of the main work then I'll try to get this implemented as part of v2.0.0