Add Google Tag Manager in WordPress with hooks and actions

wp-google-tag-manager

<?php
/* ADD GTM TO HEAD AND BELOW OPENING BODY */

add_action('wp_head', 'google_tag_manager_head', 20);
function google_tag_manager_head() { ?>
  <!-- Google Tag Manager -->
  <script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
  new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
  j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
  'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
  })(window,document,'script','dataLayer','GTM-XXXXXX');</script>
  <!-- End Google Tag Manager -->
<?php }

add_action('tb_before_header', 'google_tag_manager_body', 100);
function google_tag_manager_body() { ?>
  <!-- Google Tag Manager (noscript) -->
  <noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-XXXXXXX"
  height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
  <!-- End Google Tag Manager (noscript) -->
<?php }