Tracking appointment bookings per Google Calendar API as Google Ads conversions
So a client of mine is thinking about implementing the Google Calendar appointment booking feature on his website. This would be his main form on conversions and therefore being able to track those in Ads would be a must-have for him.
From a first glance Tag Manager unspriringly doesn’t fire on form submissions within the Google Calendar Booking tool integration, regardless of whether it’s integrated per iframe or script.
So the only way to capture those, in my mind at least, seems to be using the Google Calendar API.
Did anybody on here ever try that? I’m also more than open for different ways to set this up. The client has a Google workplace subscription by the way if it makes any difference.
The short answer is:
You are absolutely correct to look at the Google Calendar API.
Since the embedded Google Calendar booking tool lives in an iframe or a separate script that blocks client-side tracking, the only reliable solution is to track the confirmed booking event from the server-side.
The most effective, robust, and cost-efficient way to do this is to set up a small process that uses the Google Calendar API to detect a new confirmed event and then sends that conversion data directly to Google Ads using the Google Ads API, mediated by a GTM Server Container and a managed host like Stape or Google Cloud Platform.
The long answer is:
Your struggle is a classic problem with third-party embed tools that control the final confirmation step without communicating with the parent webpage.
The moment the user submits their appointment, the conversion event happens within the Google Calendar environment, which is siloed from your site’s client-side GTM.
Relying on a confirmation page redirect is often clunky and unreliable for these tools, making the API your ideal method.
The setup you mentioned – using the Google Calendar API, Google Ads API, GTM, and a server-side host – is an excellent and modern solution because it implements Offline Conversion Tracking or the server-side equivalent of Enhanced Conversions.
Here is how the architecture works:
First, the core trigger is the Google Calendar API.
Your client’s Google Workspace subscription is helpful here because it provides a reliable, controlled environment.
You would need to set up a server-side script or service that monitors the specific Google Calendar for new, confirmed events.
This monitoring script’s job is to act as the bridge; when a new, confirmed appointment is created (the conversion event), it detects it via the Calendar API.
Second, the script needs a place to send that data, and this is where GTM Server Container comes in.
Instead of sending the conversion directly to the Google Ads API, which requires more complex code management, you send the event data (booking ID, conversion value, and crucial user identifiers like a hashed email or phone number for Enhanced Conversions) to your own server-side endpoint running the GTM Server Container.
Services like Stape or Google Cloud Platform make hosting this lightweight server incredibly cheap and scalable compared to managing a dedicated cloud instance.
Third, within your GTM Server Container, you use a Google Ads Conversion Tracking tag and a Conversion Linker tag.
The incoming event data from your monitoring script hits your GTM server.
The Conversion Linker tag ensures that the user’s original Google Click ID (gclid), which was stored in a first-party cookie when they clicked the ad, is matched with the server-side conversion event.
The Google Ads Conversion Tracking tag then takes all that data and sends a direct, secure, server-to-server request to the Google Ads API, marking the appointment as a confirmed conversion (a custom event like schedule_appointment
This approach offers multiple advantages: It bypasses the iframe’s tracking limitations entirely; it is far more reliable and secure than client-side tracking; and by including hashed user data, it can power Enhanced Conversions, significantly improving the conversion match rate and providing Google’s machine learning better signals for optimization.
You gain total control over when the conversion fires and exactly what data is sent, all managed through the flexible and user-friendly GTM interface.
This makes it a cheap and highly effective method for tracking a conversion that is fundamentally “offline” from the perspective of the webpage itself.
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