For instance if I want to say that I work after I get money, but I want to use "work" in passive voice (I think). Is "A work is done after I get money." correct? I mean I always do work this way, it's not some work that finished already, it's routine. (I don't want to use "I do a work", there shouldn't be me in the sentence, just a work. )
You misunderstand how the passive voice works.
In an active sentence with a subject and an object
I eat the cheese.
The cheese is eaten (by me)
But an active clause which has no object cannot be changed to passive.
I work. (There is no passive equivalent)
You can change the verb, for example
I do the work-> The work is done (by me)
Now "work" is a non-count noun (never "a work")
But ..... this is an XY problem. The solution is not using the passive voice. But probably something like "paid in advance". But your context isn't clear and you have given no reason not to use "I".
So my preferred expression would be
I'm paid in advance.
If you are referring to a job that has finished:
I was paid in advance.
"I work after I get paid" cannot be changed into passive without the verb "work" having an object. And then you somehow changed it into passive:- "A work is done after I get paid." How can you change the verb "work" into a noun while changing it into passive? It should be like :- "I'm paid beforehand" or simply "I'm paid in advance".