Please, make sure you are hired by the client and have an active contract under your My Jobs tab before you start working on the assignement. That way the client will be able to pay you via Upwork.
@Jose N wrote:
I am doing something wrong?.
If you did work without being hired and having a contract and tracking your time (for hourly jobs) or having funded milestones (for fixed rates) then yes, you are doing something wrong.
It's called "Working for free..."