WooCommerce checkout ‘internal server error’ fail to load ?wc-ajax=checkout

Solution:

A 500 error could be caused by many things. Do you have access to your apache/php error logs? That’s the quickest way to figure it out in most cases.

Please write this in your wp-config.php

define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_LOG', true );

once you see and resolve the error, please remove or comment this code.