I've created the following code in order to include navigation buttons at the top of my Tutor LMS courses. Their purpose is that the user can navigate between courses in a category. However, I can only get the buttons to appear on a 'course' page. It doesn't display on 'lesson' pages for some reason? I wonder if anyone could help? Thank you

 function tutor_navigation_buttons() {
        global $post;

    if (!$post) {
        return "No global post object found";
    }

    $post_type = get_post_type($post);

    // Adjusted: Check if post type is "courses", "tutor_lesson", or "lesson"
    if ($post_type === 'courses') {
        $current_post = $post; // Course page
    } elseif ($post_type === 'lesson') {
        $course_id = get_post_meta($post->ID, '_tutor_course_id_for_lesson', true);
        if (!$course_id) {
            return "No associated course found for this lesson (Lesson ID: {$post->ID})";
        }
        $current_post = get_post($course_id); // Get the parent course
    } else {
        return "Not on a course or lesson page (Detected post type: $post_type)";
    }

    // Extract module number from course title
    $current_title = get_the_title($current_post->ID);
    if (!preg_match('/Modiwl (\d+):/', $current_title, $matches)) {
        return "Could not extract module number from: $current_title";
    }

    $current_number = (int) $matches[1];
    $categories = wp_get_post_terms($current_post->ID, 'course-category', ['fields' => 'ids']);

    // Find Next and Previous Modules
    $next_module = get_adjacent_module($categories, $current_number + 1);
    $prev_module = get_adjacent_module($categories, $current_number - 1);

    // Start output
    ob_start();
    echo "";

    if ($prev_module) {
        $prev_link = get_permalink($prev_module->ID);
        echo "Modiwl blaenorol";
    }

    if ($next_module) {
        $next_link = get_permalink($next_module->ID);
        echo "Modiwl nesaf";
    }

    echo "";

    return ob_get_clean();
}

add_shortcode('tutor_navigation', 'tutor_navigation_buttons');

// Helper function to find the adjacent module by number
function get_adjacent_module($categories, $target_number) {
    $args = [
        'post_type'      => 'courses',
        'post_status'    => 'publish',
        'posts_per_page' => 1,
        'tax_query'      => [
            [
                'taxonomy' => 'course-category',
                'field'    => 'id',
                'terms'    => $categories,
            ],
        ],
        's' => "Modiwl $target_number:",
    ];

    $query = new WP_Query($args);

    if (!$query->have_posts()) {
        return null;
    }

    return $query->posts[0];
}