Limit Job Listings to One Per User

functions.php

add_filter( 'submit_job_steps', function( $steps ) {
    $user = get_current_user_id();
    if ( ! $user || current_user_can( 'manage_options' ) ) {
        return $steps;
    }

    $user_post_count = count( get_posts( [
      'author' => $user,
      'post_type' => 'job_listing',
      'post_status' => [ 'publish', 'pending' ]
    ] ) );
    if ( $user_post_count > 0 ) {
        $steps = [
            'warning' => [
                'view' => function() {
                    echo __( 'Sorry, you can only post one job listing at a time.', 'wp-job-manager' );
                }
            ]
        ];
    }

    return $steps;
} );