Connection amp-form event to Google Tag Manager Ads-conversion tag

I have a site with an amp-form. I want to track Google Ads conversions using amp-form's amp-form-submit-success event as documented here.

Google Tag Manager's AMP container seems to only support a few triggers like Click, Scroll, Timer etc. No custom trigger. I have therefore created a Ads Conversion tag without a trigger in the hope that I can somehow manually trigger it from the <amp-analytics> tag configuration itself.

One thing I've tried is add the the adwords tag directly into the <amp-analytics> config like this:

    <amp-analytics config="https://www.googletagmanager.com/amp.json?id=GTM-123456&gtm.url=SOURCE_URL" data-credentials="include">
      <!-- Extra tag for form submission  -->
      <script type="application/json">
      {
        "vars" : {
          "gtag_id": "GTM-123456",
          "config" : {
            "GTM-123456": { "groups": "default" },
            "<Conversion ID>": { "groups": "default" }
          }
        },
        "triggers": {
          "C_fm2EfIAdnpI": {
            "on": "amp-form-submit-success",
            "vars": {
              "event_name": "conversion",
              "send_to": ["<Conversion ID>/<Conversion Label"]
            }
          }
        }
      }
      </script>
    </amp-analytics>

The code above is based on the installation code generated for me by Google Ads. I've just tried to replace the click event with the amp-form event. This is the standard code:

    "C_fm2EfIAdnpI": {
      "on": "click",
      "selector": "CSS_SELECTOR",
      "vars": {
        "event_name": "conversion",
        "send_to": ["<Conversion ID>/<Conversion Label"]
      }
    }

I get an error from my code saying that the trigger is lacking a request property (which it is). But I have no idea what that request url would be.

Has anyone managed to hook up amp-form-submit-success to Google Ads Conversion? With or without using Google Tag Manager?

Do GTM AMP containers only support the built in Click, Scroll, Timer (etc) triggers and nothing else?

You can access the requests GTM provides you if you just open the JSON file in the config url. In your example: https://www.googletagmanager.com/amp.json?id=GTM-123456&gtm.url=SOURCE_URL (I would suggest you don't share your GTM id here).

If you created any triggers in you GTM console you'll get a requests property with a list of endpoints for each trigger. So you can create a "fake" trigger and then just use that request.