It can indeed be difficult for a freelancer when he has completed all the work that was requested, submitted it, received payment... but there is still this fixed-price contract hanging out there, with no milestones...
Sometimes there isn't much you can do about it. Maybe the client picked up the files they needed and simply doesn't use Upwork any more. Maybe they aren't receiving any messages you send through the messaging system.
I don't like to pester clients. I don't think it is effective or welcome. So I don't try to send additional messages to client.
But one thing I do on a regular basis, is if the client contacts me and asks any questions or requests anything, then I use that as an opportunity to ask the client to close the contract.
For example, the fixed-price project may be completed and paid for, but the client may have one last question or request:
"Preston:
Thank you again for your work on this. Everything works great. I know you did everything in the agreement already, but I would like to see the project with the headlines in red. Do you think you could do that?"
"Gary:
That sounds like something worth looking at. It's technically not part of the original specs, but that's okay. If you will go ahead and close the contract, then I'll send you a version with that modification and you will be able to use whichever you prefer."
[Obviously if there is significant work involved, I won't just do it for free, but I would ask the client to close the current contract AND set up a new contract for the new work. But for something simple, I can use that as a way to motivate the client to close the contract.]
