Check log file
If you enabled logging in section General Settings, you can download the log file using the link:
Stores → Configuration → Sales → Payment Methods → Other Payment Methods → Worldline → General Settings → Download log file.
The log file contains all messages to and from the Worldline servers and may help finding the cause.
In case of questions or problems that cannot be resolved with the Magento® manual or the Worldline guide, please contact your account manager or implementation manager at Worldline.
You can also contact us by scrolling a bit down on our site and filling out your details.