The payment form works fine with a dummy gateway, but when I switch to the Mollie payment gateway (live key) the payment form just refreshes the page. The error flash is "Invalid payment or order. Please review.". This same message pops up once in the CMS. There are no details of this in the log.
How do I check where the error occurs and how to fix this?
Edit: the transactions tab of the order in the CMS is empty