Our connector is sending requests to the Prestashop API. In some cases (due to bugs in Prestashop specifically with some custom installed plugins) error is happening on the Prestashop side. Unfortunately Prestashop API is not returning the exact error message so we cannot display it so it will be clear what happened.
To see detailed error logs you need to go to Prestashop error logs (ask your Presta developer for them). And inside the error logs of Prestashop there is error message explaining the reason.
For example, like below
[PHP Warning #2] Attempt to read property "php_self" on null (/home2/xxx/public_html/modules/estimateddelivery/estimateddelivery.php, line 2809)
Prestashop developers by reading the above error can understand what should be fixed on the Prestashop side. In the above example, most likely problem in custom module “estimateddelivery” that has bug.