Hi team , I am integrating Google analytics with growthbook . My question is how will google analytics know from which variant the purchase has happened. ?

Are you connecting GrowthBook to BigQuery or directly to GA? If using BigQuery, we use a combination of date and user ids. If we see someone saw an experiment and then converted 10 minutes later, we attribute that conversion to the experiment. If using GA directly, we rely on custom dimensions. When someone sees an experiment, you would set a custom dimension that would then automatically get added to all future tracking calls.

I am using big query

In the tracking callback for the SDK, you just need to track a new GA event called something like "viewed experiment" and pass the experiment id and variation id as event parameters. You don't need to do anything else to your existing events like purchase.

I tried the same method , but I wasn’t able to see any revenue related data on my growthbook dashboard . I mean revenue is still 0 . What might be the problem ?