Why WordPress admin-ajax.php calls return 0

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You will see that kind of error if you are developing a custom WordPress plugin that makes Ajax calls.

A normal response to an Ajax call should be a JSON object that contains some useful information.

The reason could be that the action is not being handled properly. The plugin must send exactly at least the action parameter, and depending on its value, WordPress will trigger the appropriate hook.

action=wpsandbox_cool_plugin_my_ajax_action

How to properly hook for Ajax requests in WordPress

// Hook the function to handle logged in users
add_action('wp_ajax_wpsandbox_cool_plugin_my_ajax_action', 'wpsandbox_cool_plugin_name_process_ajax'');

// handle guests (non-logged in users
add_action('wp_ajax_nopriv_wpsandbox_cool_plugin_my_ajax_action', 'wpsandbox_cool_plugin_name_process_ajax'');

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