Redirects users back to the previous page when accessing a restricted LearnDash lesson

wpf-redirect-to-previous-lesson.php

<?php
/**
 * Redirects users back to the previous page when accessing a restricted LearnDash lesson
 *
 * @param string $redirect_url The redirect URL
 * @param int    $post_id      The post ID
 * @return string The modified redirect URL
 */
function my_learndash_redirect( $redirect_url, $post_id ) {

    // Check if it's a LearnDash lesson
    if ( get_post_type( $post_id ) === 'sfwd-lessons' ) {
        
        // Optional, disable the generic redirect and take them back to the course:
        // return false;
        
        // Get the previous page URL
        $previous_url = wp_get_referer();
        
        // If we have a previous URL, use it
        if ( ! empty( $previous_url ) ) {
            return $previous_url;
        }
    }

    return $redirect_url;
}
add_filter( 'wpf_redirect_url', 'my_learndash_redirect', 10, 2 );