If a client hires you using an hourly contract, then you are automatically paid for the time that you log working on his behalf.
If this is a fixed-price contract, then you are supposed to send the client the work, using the official Submit Work / Release Payment button,
If the client does nothing, you will be paid AUTOMATICALLY.
And the client can not decide to not pay you unless YOU agree to his decision.
So the short answer is: No.
The client can not simply refuse to pay you. As long as you use Upwork properly, then you will be paid. This means you use hourly contracts properly or, if using fixed-price contracts, you ONLY do work on milestones which are fully funded.
re : "If i send a client my copywrite work and ask if its good enogh"
The client hired you because you present yourself as a professional. You really should not be taking on work that you do not know how to do. So you do not ask the client if the work is good enough.
You do not "send the client the work and ask if it is good enough."
You finish the assignment, and you look it over yourself. When the work is done, then YOU are the one who decides it is done.
You then submit the work using the "Submit Work / Request Payment" button. This presents the work to the client AND GIVES HIM AN OPPORTUNITY to request changes.
That is how the button works. If you separately send messages then you are generating redundant communications and not using the Upwork user interface as intended.