Google Tag Manager Server-Side gtm.js returns 404

I created a new Server-side GTM Container, set up Google App Engine, added a GTM Client, and have everything deployed. However, when I check the gtm.js for the container the file returns a 404.

So I created the the App Engine instance using the automatic configuration and it returns ok for the /healthy path.

The GTM container is published and has an active tag and trigger. Here is a screenshot of the GTM Client.

I have this snippet added to my site:

<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://gtm-p3vlp32-ndhiz.uc.r.appspot.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
})(window,document,'script','dataLayer','GTM-P3VLP32');</script>
<!-- End Google Tag Manager -->

Then I get this error in the network tab. Did I miss a step to get the gtm.js file to be returned?