Collect tracking code implemented via Google Tag Manager should have some difference compared to the documentation? Asking that because is Not showing under the status Tab in Einstein predictive email. Any suggestions?
You need to have the different parameters present in your Data Layer, and fetch it from there, within Google Tag Manager. These need to be created as variables, before they can be included in the Collect Code.
The specific implementation details will differ, based on the structure of the Data Layer, so it is difficult to provide an exact specification which you can apply directly.
If you believe your Collect Code is implemented correctly in Google Tag Manager, you can verify use it Chrome Developer Tools. After opening it, go to Network tab, and put igo in the search box. This will show you any calls being made to Collect Code/Marketing Cloud. See an example of this below. This is actually from an implementation where Collect Code is implemented using Google Tag Manager: