This is the respective issue as https://www.drupal.org/project/drupal/issues/2245767, and would be a good addition to the features of our layouts system.
Problem/Motivation
Some blocks, like user login, should be shown on 403/404 response pages. Others, like the help block, should not.
Proposed resolution
Add a visibility setting to blocks that restricts visibility to any combination of 200/403/404 responses. Default this to show the block for all responses.
Perhaps in our case it also makes sense to add that visibility conditions to the layouts (besides blocks), so that if people really have the need for it, they can configure a different layout to be used based on response.
Recent comments
Thanks! I tested PayPal WPS (since I also use it in my Drupal 7 Commerce shop). With the PayPal server SANDBOX mode (no real payment transaction, just simulated). And everything...
Commerce shop system from Drupal
Peter, I've done an initial port of Commerce PayPal. While I haven't tested it, I think it should work, as the module is not too complex. https://github.com/backdrop-contrib/...
Commerce shop system from Drupal
Glad you finally found it! Someone really needs to port commerce_paypal.
Commerce shop system from Drupal