Why in the Impact analysis, when selecting metrics, are there only event counts, user counts, and event property aggregations available? There are no user-granularity aggregation metrics, nor are there rolling windows.
Presumably the payments are tracked on payment events with the amount as a property on the event? Then you can do an aggregate by user insight of the event. Aggregating the sum of the payment amount property. And then breakdown the insight by user (id, name, email, whatever field you are using).