Tracking Resource Form Submission (Popup Form) Event in GA4 via GTM (Gatsby.js)

Objective

Track form submissions from the resource section popup as a GA4 event (generate_lead) using Google Tag Manager, even though there is no page reload or thank-you page.

Why This Approach?

Since this is a JavaScript-powered popup form, GTM’s default Form Submission trigger likely won’t detect it.

👉 The most accurate solution: fire a custom GTM event using dataLayer.push() after a successful submission.

Step 1: Add dataLayer.push() to Your Form Logic

Ask your developer (or update the Gatsby form component) to push an event after successful submission, like this:

window.dataLayer = window.dataLayer || [];

window.dataLayer.push({

  event: “generate_lead”,

  form_location: “popup_resource_form”

});

Place this code after the form data has been successfully submitted and accepted, not just when the submit button is clicked.

Step 2: Create a Custom Event Trigger in GTM

1. Go to GTM
2. In the left menu, go to Triggers
3. Click New
4. Name it: Custom – generate_lead (Resource Popup)
5. Choose Trigger Type → Custom Event
6. Set Event name to: generate_lead
7. Choose: All Custom Events
8. Click Save

Step 3: Create a GA4 Event Tag

1. Go to Tags → Click New
2. Name it: GA4 – generate_lead (Resource Download)
3. Tag Configuration → Select GA4 Event
4. Select your GA4 Configuration Tag
5. Set Event Name to: generate_lead
6. Add optional parameters (for context):
   form_location : popup_resource_form

         resource_type : whitepaper

Step 4: Link the Trigger to the Tag

1. Scroll to Triggering
2. Select: Custom – generate_lead (Resource Popup)
3. Click Save

Step 5: Preview and Test

1. Click Preview in GTM
2. Open the Resource page on your website
3. Click Download this file → Form appears
4. Fill out and submit the form
5. In the Tag Assistant debug window, confirm:
   • Event generate_lead appears in the timeline
   • GA4 event tag fires successfully
   • Event parameters (form_location, resource_type) show up correctly

Step 6: Publish

Once confirmed, click Submit → Publish in GTM
Name the version: GA4 Event – Resource Popup Submission

Result

Each time a user submits the popup resource form, a GA4 event generate_lead is triggered, helping you:

• Track downloads
• Attribute leads to specific campaigns or files
• Build conversion-based audiences in GA4