CB Paid Subscriptions

See the below for further guidance. Seams entire subscription creation and payment handling process will need further changes.

https://stripe.com/docs/billing/migration/strong-customer-authentication#upgrading-integration

Appears creating the subscription first with payment_behavior=default_incomplete will return a pending_setup_intent in the subscription object which can be used for payment. Effectively don't need to manually create a payment intent or setup intent for recurring payments then.

Best approach seams to be to just replace the PaymentIntent with a SetupIntent when the payment is for a recurring subscription. This avoids creating a plan, customer, and subscription object for a payment that may be cancelled (e.g. backing out of the pay form).