I found a way:
This is for QBOL, not sure if other versions works the same way, might.....
I had to move to the Plus version, where you have a couple more functionality, one if them is Projects.
With this func. on you can create one or multiple different projects under one customer.
With this you can create an estimate, turn it into an invoice (or multiple partials), receive payment(s) and assign costs to each project. Then you can pull performance reports for the client (summary will show total for the client) or open per project .
I hope this helps,