How to use google tag manager with gatsby

I'm using gatsby and the gatsby-plugin-tag-manager and I'm having trouble getting custom events to trigger. My gatsby-config.js looks like this:

    {
      resolve: `gatsby-plugin-google-tagmanager`,
      options: {
        id: 'GTM-XXXXXXX',
        includeInDevelopment: true,
        defaultDataLayer: function() {
          return {
            pageType: window.pageType,
            // platform: 'gatsby',
          }
        },
      },

When I run everything locally, I can get my events to trigger properly using this code:

window.dataLayer.push({
  event: 'gatsby-course-splash-sign-up',
})

The problem is that when I deploy it statically to an s3 bucket instead of running on a server, while the page views trigger, nothing else does. Does anyone know how to get custom triggers to work? Thanks!