WordPress action hook for sending a Post ID custom dimension value to Google Analytics.

post-id-custom-dimension-action-hook.php

<?php

add_action( 'wp_head', function () { 
  if (is_single ()) { 
?>
  <script>
	// Post ID Custom Dimension Snippet
	let dimension9Value = '<?php echo get_the_id() ?>';
	//ga('set', 'dimension9', dimension9Value);
	ga('send', 'event', 'dimension', 'Post ID', {
  		'dimension9': dimension9Value
	});
  </script>
<?php
  }
} );