The module is working fine, thanks a lot @bessone ;)
During the check-out, the user is redirected to the Satispay page.
In this page, if the user clicks on the X (closing button) without paying, the user is sent back to Drupal and the order is set to "completed".
The order is stored correctly and the payment is set to "pending".
The user's intention here is to cancel the payment, not to complete the order without paying.
It would be nice to put back the order to the cart stage and present a warning message "Your payment failed, please try again".
Thanks a lot!
Fixed
1.0
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
I am closing the problem, I have been using the module for a long time now and do not experience any problems.
Version 2.0.0 uses a different authentication system for Satispay that cannot be backwards compatible.
For those who are still using 1.x (Drupal 8) to uninstall the module and re-install it in version 2 proceeding to the new key exchange with Satispay.