When going from a test to live environment, mollie redirects to their own thank you page instead of the redirect url provided via the API. In the test environment the redirect works. The paymnet is an iDEAL payment via QR code.
The documentation states:
"Note that after the payment, the customer will also be redirected to the redirectUrl on the mobile device for some payment methods (such as iDEAL). For Bancontact, a special thank you page is shown on the mobile device."
It seems that in my case the customer is redirected to the special thank you page of Mollie instead of our redirectUrl