Google Analytics Global Site Tag (gtag.js) for Facebook Instant Articles (Full Snippet)

gtag4fbia.js

<figure class="op-tracker">
  <iframe>

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

    gtag('set', 'page_title', 'FBIA: '+ia_document.title);
    gtag('set', 'campaignSource', 'Facebook');
    gtag('set', 'campaignMedium', 'Social Instant Article');

    gtag('config', 'UA-XXXXXXXX-X');
  </script>

  </iframe>
</figure>

I tried to use campaignSource and campaignMedium but it didn't set properly.

It seems the campaign data should be:
campaign_source
campaign_medium

As mentioned here
https://support.google.com/analytics/answer/11259997?hl=en

The link you shared is for Google Analytics 4. This gist is five years old and was correct at the time for GA Universal.

Thanks for sharing though!