Use [primary_category] to display SEOPress Primary Category

*SEOPress Primary Category Shortcode.php

<?php  //ignore this line - for gist formatting

function get_primary_category_name() {
    // Get the post ID of the current page
    $post_id = get_the_ID();
    $cat_id = get_post_meta($post_id, '_seopress_robots_primary_cat', true);

    // Validate and get the category name
    if (!empty($cat_id)) {
        $term = get_term($cat_id, 'category');
        if (!is_wp_error($term) && !is_null($term)) {
            return $term->name;
        }
    }

    // Fallback - Fetch the first category if a primary category is not set or is invalid
    $categories = get_the_category($post_id);
    if (!empty($categories) && !is_wp_error($categories)) {
        foreach ($categories as $category) {
            if (!empty($category->name)) {
                return $category->name;
            }
        }
    }
    
    return; // Return null if no categories found
}
add_shortcode('primary_category', 'get_primary_category_name');