Install and QA custom tracking codes.
A large orange banner at the top of the page indicates you are now in preview mode.
Click Refresh below the orange banner to effect all the changes you may have made to your tags in your GTM Workspace.
After making changes to your tags, GTM may not capture these changes immediately, this is where refresh comes in. Refresh basically helps to update your GTM workspace. Always click on this any time you switch to preview mode.
If you do not see the tag manager window after reloading your site, you can tell something is wrong and you may need to check if you missed any of the steps in setting up your tag. Click around on your website to further test. Go through the pop-up, check the summary to see if the tags you set up fired correctly. This window will only pop up on your computer, it will not be shown to your visitors.
Click on the tag name on the Tag manager window and check for
gtm.js which is the page view event in GTM. You can also click on Page view on the Summary pane to the left.
gtm.js code does not change according to tags. It is a general code for all GTM Page view events. Scroll down and check under Firing triggers for
gtm.js. This section will also show you where the hit was fired and how many times it was fired. Check that details such as the script, trigger, and track type are exactly the way you set them up.
Verify with the platform you created the custom tag for, and check that the hit recorded in GTM is also received by the platform.
A custom tag for a platform like Facebook can be verified by installing the Facebook Pixel Helper for Chrome. After installation, click on it to see if the tag is working. A green button tells you the tag is all good. It will also tell you if there is any issue with your tags.
After thorough testing and verification, make sure you publish your tags and get them live. Publishing will allow the latest changes in the GTM container to go live and track all visitor actions on your website, not only yours.