A Google Ads conversion tag can show the status failed in GTM Preview mode or Tag Assistant, even though the conversion was sent and tracked successfully. This page explains why, and how to confirm your tracking works.
This is a false error. It's a technical quirk of how image-based tracking and browsers interact, and it doesn't mean your conversion tracking is broken.
Why it happens
When a Google Ads conversion tag fires in GTM, it sends a request to https://www.googleadservices.com/ccm/conversion/<Conversion ID> by loading it as an image in the browser.
Google receives and processes the request correctly, but responds with an empty text/plain response instead of an actual image (image/gif). The browser therefore thinks the image failed to load. GTM Preview relies on that browser feedback, so it marks the tag as failed.
When the request is made
This request is only made under certain conditions, and is directly tied to the values stored in the _gcl_au cookie. This cookie can be created by:
- The Conversion Linker tag in GTM
- The Google tag, implemented via GTM or directly on the page
- The User-provided data event tag in GTM (a separate event, on a page containing personal data, before the conversion)
The _gcl_au cookie can also be modified to hold a longer value with more information.
Good to know: The request includes the auid parameter, the Advertiser User ID: a unique pseudonymous ID for the user, which matches the value in the _gcl_au cookie.
How to confirm the tag works
If you see this status, check whether the conversion actually arrived:
- Network requests in your browser's developer tools
- Conversion logs in Google Ads
- Tag diagnostics in Google Ads, or via your enhanced conversions setup
Related pages
Google Ads failed for no reason: a false failed status caused by a cookie prefix mismatch
Guide on fixing errors GTM client-side
What is considered an error?