[tothrowaway]

That window between the last two steps is a killer. PayPal Checkout supports iDeal, and I get complaints about how PayPal took their money, but their account (on my system) was never setup...because I never got the money/notification from PayPal! It drives me nuts.

PayPal seems to refund them after a certain period of time automatically, but it takes a while. Naturally, the customer is anxious and mad at me, and not likely to risk checking out again.

[Doxin]

A proper iDeal integration doesn't break in that scenario. I'm not entirely sure as to how it's implemented technically, but if you do iDeal right it works even if you never click the "back to merchant" button.

E.g. when working with stripe to integrate iDeal you'll want to listen for payment complete webhooks, in addition to dealing with the user coming back from the iDeal page.