When your website releases WordPress internal server error 500, you will see that the server is not responding. It happens when you are migrating your existing site to new hosting. In such a situation, the PHP version that is associated with your server can get a server 500 error./ You need to take the back up of all your themes and plugins of the old site and then delete one by one. After that enable them one by one, that will solve the issue
You can also regenerate your .htaccess file so that error can be fixed
The wrong placement of PHP code can occur 500 error, so you need to correct codes through experts.