Improve tag tracking on your website.
Visit your home page or any page on your website that has Google Tag Manager code installed.
Right-click with your mouse and select View page source or press Ctrl + U on Windows or Command + Option + U on MacOS.
The browser will display the code for your page.
Use Ctrl + F on Windows or Command + F on Mac to open the search bar and type “gtm.js”.
You should see at least two instances of gtm.js on your page.
Open Google Tag Manager and select container, then click on the Preview button, in the top menu bar.
Type the URL of the page that should be firing tags and click on the Start button. You may need to refresh the browser window.
A new debug console window will open to load your URL. After it has loaded your page, go to the Google Tag Manager window to evaluate what tags are being fired on the page and which ones are not fired.
Look at the tags fired and those that were not fired, and decide whether the right tags were fired on your page. Click on the Error tab to see any tags that failed and the error message that was recorded.
Keep that information in mind to fix any tag that shows up in the Error section.