First of all: Paypal and SEPA bank transfers in the EU work just fine.
Due to ongoing issues with cancelled credit card payments due to „The customer returned from Stripe and changed the cart details.“,
we have now switched from redirecting to a payment page hosted by Stripe to having the credit card payment embedded.
So far Stripe support can’t see anything wrong on their side and we don’t see anything out of the ordinary on our side. So let’s hope this randomly solves the elusive issue.