Is the PowerPack Registration Form widget not working on your WordPress websites?
This article will explain how to solve the "Elementor Registration Form Widget Not Working" and "Server Error" issues.
Why does the Internal Server Error occur?#
When the post_id parameter doesn't have any value, it produces a 500 Internal Server Error and enables the registration form widget to work properly.

How to Fix the Registration Form Widget Issue?#
Step 1: Add the below code into wp-config.php
// Excludes arguments from stack traces generated from exceptions.
@ini_set( 'zend.exception_ignore_args', 0 );

Step 2: Update the Registration Form widget page.
Step 3: Clear Cache
Done!
If the issue persists, please feel free to contact our support team. Hope this helps!