add_action('wp_head', 'insert_custom_ga4_tag');
function insert_custom_ga4_tag() {
// Only run on single posts
if (is_single()) {
global $post;
// Retrieve the custom field value
$ga4_id = get_field('ga4_measurement_id', $post->ID);
// If an ID exists for this post, output the GA4 tracking script
if (!empty($ga4_id)) {
?>
