If it’s a 500 internal server error, something should be logged to the server’s error logs telling you what the error was. If you can’t find error logs in your hosting control panel, you can enable WordPress to log errors to wp-content/debug.log file:
You can also enable WP_DEBUG in your wp-config.php file to write to a debug.log file that will be located at /wp-content/debug.log by setting the following values in the wp-config.php file:
define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
More information can be found at the link below, or by contacting your hosting company:
https://codex.ww.wp.xz.cn/WP_DEBUG
Enable the debug logging, then submit on site again to cause the error to happen again, and then check that file
These are the error it throws
PHP Warning: Use of undefined constant ‘xmlrpc_methods’ – assumed ‘‘xmlrpc_methods’’ (this will throw an Error in a future version of PHP) in /var/www/wp-content/themes/listify-child/functions.php on line 274
Error Table ‘g9n642721548595.wp23_comments’ doesn’t exist de la base de datos de WordPress para la consulta SELECT SQL_CALC_FOUND_ROWS wp23_comments.comment_ID FROM wp23_comments WHERE ( ( comment_approved = ‘1’ ) OR ( user_id = 4 AND comment_approved = ‘0’ ) ) AND comment_post_ID = 73 AND comment_parent = 0 AND comment_type != ‘order_note’ AND comment_type != ‘webhook_delivery’ ORDER BY wp23_comments.comment_date_gmt ASC, wp23_comments.comment_ID ASC realizada por require(‘wp-blog-header.php’), require_once(‘wp-includes/template-loader.php’), include(‘/themes/listify/page-templates/template-single-column.php’), comments_template, WP_Comment_Query->__construct, WP_Comment_Query->query, WP_Comment_Query->get_comments, WP_Comment_Query->get_comment_ids
Error Table ‘g9n642721548595.wp23_comments’ doesn’t exist de la base de datos de WordPress para la consulta SELECT SQL_CALC_FOUND_ROWS wp23_comments.comment_ID FROM wp23_comments WHERE ( ( comment_approved = ‘1’ ) OR ( user_id = 4 AND comment_approved = ‘0’ ) ) AND comment_post_ID = 73 AND comment_parent = 0 AND comment_type != ‘order_note’ AND comment_type != ‘webhook_delivery’ ORDER BY wp23_comments.comment_date_gmt ASC, wp23_comments.comment_ID ASC realizada por require(‘wp-blog-header.php’), require_once(‘wp-includes/template-loader.php’), include(‘/themes/listify/page-templates/template-single-column.php’), comments_template, WP_Comment_Query->__construct, WP_Comment_Query->query, WP_Comment_Query->get_comments, WP_Comment_Query->get_comment_ids
[08-Aug-2019 17:35:20 UTC] PHP Notice: Undefined index: checked_calc_value in /var/www/wp-content/plugins/ninja-forms/includes/Fields/Checkbox.php on line 133
I’m not convinced that the error messages you quote there are actually related to the issue you’re seeing, BUT they do mention an issue with your theme; in particular, they mention the /themes/listify/page-templates/template-single-column.php file. Try switching to a different theme temporarily to see if the issue goes away or not. Let me know how it goes!
I’m marking this thread as Resolved as it’s been more than a month since the last reply. If you still need help, please do reply again and mark the thread as Unresolved!