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GrowthBook only has access to the attributes that are set in your app (Next.js). In our Next js example, you can see that the ​`id`​ is being set and passed to GrowthBook.

Thanks for the reply Ryan! So, it is not mandatory to pass deviceId (GrowthBook attribute) to GoogleAnalytics. Correct?

Right. However, you do need to set some kind of unique ID as shown in the example. Of course, if you're not passing a deviceId, then you can't use it in experiments or flags, as you mentioned.

Got it. The last question about is about id. Is there any benefits/preference to use id over deviceId in the experiments?

This is a good breakdown: https://docs.growthbook.io/faq#what-do-i-use-for-an-id-attribute-in-the-sdk-if-my-users-arent-logged-in