You may capture Revenue(amount) via Products Variable String.
You would need to populate price in products syntax with Purchase Success Event(s.events = "purchase";) to capture it in Revenue metric successfully.
If you do not want to capture the amount with purchase event, then you may also use custom implementation by populating the specific values into currency events.
s.events = "event1=9.99";
Hope this helps.
Let me know in case of any further queries.