I'm working on an interesting project and just about done. But, the client is refusing to put the final payment into escrow, even though he's received the work. What can I do?
re: "What can I do?"
You can learn from your mistake.
If there is no money in escrow, then there is nothing you can do. There is nothing you can dispute. The client has ALREADY released all of the money from escrow to you.
Anything that happens at this point is strictly between you and the client.
In the future, do not work on an unfunded task.
And be sure to include in your feedback for this client your experience with not getting paid in full, if your client doesn't find a way to pay you via Upwork's system.
Yes, you should have known that under Upwork's rules only money in escrow is considered by Upwork to be "due" to a freelancer, so make sure all money you are expecting to be paid under hourly projects is fully funded in escrow before you send a client completed work.
If the project has multiple milestones set up on Upwork for work completion and client payments, each milestone should be fully funded before you submit the work for that milestone.