Rewriting a page with a custom parameter

To fix this issue, we had to add the “query variables” into the functions.php of our theme to add them to the public variables.

function add_query_vars_filter($vars){
  $vars[] = "subject";
  $vars[] = "param";
  return $vars;
}
add_filter('query_vars', 'add_query_vars_filter');

This allowed us to retrieve the variables’ value this way.

$subject = get_query_var('subject', false);