This client's GTM is now set up.
GTM-WG8S8PT
Added other team members as ADMIN, sent invites. 
Also created Optinmonster tag container, added code 
<!-- This site is converting visitors into subscribers and customers with OptinMonster - https://optinmonster.com-->
<script type="text/javascript" src="https://a.opmnstr.com/app/js/api.min.js" data-account="1962" data-user="25748" async></script>
<!-- / OptinMonster -->

Published container and set to live. 

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<!-- 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-WG8S8PT');</script>
<!-- End Google Tag Manager -->


<!-- Google Tag Manager (noscript) -->
<noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-WG8S8PT"
height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
<!-- End Google Tag Manager (noscript) -->