I purchased this theme yesterday and every time I try to install the required and recommended plugins I receive a 500 Internal Server Error. I’ve tried deactivating plugins and reinstalling. I’ve tried reinstalling theme and reinstalling WordPress. Same issue.
There maybe many reasons why you get the error. Maybe you don;t have the sufficient permissions to do that, or you have installed the theme not correctly.
Please can you show us your site credentials so we can give it a closer look?
Edit the file wp_config.php on your wp installation and change WP_DEBUG to true to make the errors display.