There can be multiple reason for this error. The first thing you should check whether or not your server fulfils all the pre requisites as mentioned in the product detail page.
You can remove all the files & folder, create an index.php file & put below line of code to get information about your server:
<?php phpinfo(); ?>
Once saved, you can try to access the URL on your domain. You should check for the PHP Version & all other extensions that are required for the script.
If everything is OK but still you are getting 500 error, you should check the error log that is usually available at storage/logs/laravel.log file.
You can share this file to hello@scriptmint.com for more information.