Sometimes on some requests you may see “PHP Notice” error. It is not allowing to send any requests to Prestashop webservice. You may see this on some older Prestashop versions because there are some issues there. Reasons an be different:
Most often reason: You have installed 3rd-party plugin and it is not well tested to work with API. And in error message (see example below) you may see exact module name that causing this issue. Like in example below you see there is some module “bolcom“. In this case you need to ask Prestashop developer to fix that bug.
prestapyt.prestapyt.PrestaShopWebServiceError: '[PHP Warning #2] Creating default object from empty value (/home/clients/cc580a72da9f40f48536085de6720fc4/sites/xxx-xxxxc/modules/bolcom/bolcom.php, line 565)'
You haven’t installed proper PHP for your Prestashop. You need to always make sure that prestashop version and PHP version correspond to each other. See here
There can be bug in Prestashop, that raises Warnings. And this warnings are blocking connection to Prestashop. The can be solved by special PHP settings (to ignore warning). Like described here