Is it possible to pay extra for the project after the contract is closed?

Question

Upwork

I took the project for an upwork budget of $180. The client is pretty new on upwork. He hired me while opening a milestone for $50. He wrote that everything is fine. When I handed over the layout, he said that everything was ok too. Communicated well too. I closed the milestone and the contract, and wrote a message: Is everything in order, has the entire budget fallen on the account. I wrote that they say not all. He replied that he would try to resolve the issue. Haven't been online for a few days.
Question: Can the customer renew a closed contract and add the remaining amount or contact support?
Sorry for the grammatical errors, writing from my phone.

Answer 1

He can send any amount as a bonus

Answer 2

can the customer renew a closed contract and add the remaining amount or contact support?

The client can add any amount as a bonus after the closing of the contract at any time.

Answer 3

Make it a rule not to start working on a new milestone until it's opened by the customer and money has been reserved, as Upwork advises. Add, as mentioned above, the customer can in the form of a bonus.

Answer 4

>Answered that he would try to solve this issue. Haven't been online for a few days.
you are not a freelancer, if you have never been thrown, congratulations on your baptism of fire.