I had problems with my backup and was asked to send error_log but I could not find it.
If you cannot find error_log neither in your FTP folder logs/error_log nor in the root of your website, we would recommend to enable PHP constant WP DEBUG that will display all PHP errors and warnings.
Using any FTP client (e.g. Filezilla) in your WordPress folder find the file ‘wp-config.php’ and set the following:
If there occurs 500 Internal Server Error then in your FTP should be created file ‘wp-content/debug.log’ that should contain all errors.
P.S. some WordPress plugins can interfere into the process of error display, even if the constant value is set to ‘define(‘WP_DEBUG’, true)’.