I enabled the Google Analytics integration and pasted in my Google Site Tag. When I hit save I got a "The page you requested does not exist" message and a Error code: 1S160/2

What am I doing wrong???

Your GA code should look like:

<!-- Google tag (gtag.js) -->
<script async src="https://www.googletagmanager.com/gtag/js?id=G-XXXXXXXXX"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());

  gtag('config', 'G-XXXXXXXXX');
</script>

This code would be inserted into: 

ACP > System > Site Features > Integrations > Google Analytics

After adding the code, you MAY need to clear your system cache.  

ACP > System > Support > Get Support

Click on "Clear System Caches".

I cleared my cache and then pasted again as per the above instructions- still  no good. 

 

<!-- Google tag (gtag.js) -->
<script async src="https://www.googletagmanager.com/gtag/js?id=UA-4567890-1"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());

  gtag('config', 'UA-567899-1');
</script>

Have you tried this with a default theme?

No, my theme is slightly tweaked. Is that a likely issue?  

Ended up having to have my server settings tweaked. 

11 minutes ago, John Horton said:

Ended up having to have my server settings tweaked. 

Sounds like mod_security or another security module was involved. Is that true?

yes exactly

13 minutes ago, John Horton said:

yes exactly

Thanks for confirming and glad to hear it’s resolved!