I'm not entirely clear what you are trying to measure but it sounds like you want to create a goal metric using a field on the user record and the field is defined as a Rollup field.
I don't think you can use the user entity for goals or indeed fields that are defined as rollup fields.
I would look to create a metric on the commission entity defined as Amount, type integer and then add the rollup fields section of the goal metric form to add the entity (commission) and the field (number of lives). There is no need for you to create
any rollup fields.
Note: defining a field as rollup field in Customization is different from adding rollup fields to a goal metric.