Error message after Mollie payment


After the Mollie payment was broken during the bank process I get the following error. Anyone know what is going on?

An uncaught Exception was encountered

Type: Omnipay\Common\Exception\InvalidRequestException
Message: The transactionReference parameter is required
Filename: /home/wesaca/
Line Number: 26

File: /home/wesaca/
Line: 610
Function: getData

File: /home/wesaca/
Line: 280
Function: send

File: /home/wesaca/
Line: 224
Function: payment_validate

File: /home/wesaca/
Line: 325
Function: require_once

update 28-3-2019:
After testing again. I get this error code also after a successful payment. It looks like the redirect URL is not OK. Where can I find this? THX Freek