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Place the Adloop tag between the initialization of your Analytics solution and the pageview event being sent
Proceed with the contener generation and make sure there are no error during the auto-test step
Publish the contener
In the case of the a single tag for initialization
If you use a single tag for initializing your analytics solution and for sending the page view event, then simply place the Adloop tag before your Analytics tag and modify your Analytics tag to include the code for populating the custom dimension. Below is an example of how you can implement it with Google Analytics 4 (add line 2 and 6 in your GA4 code) :
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