Recap: In March this year, I was frantically looking for a job and ended up accepting a 3-month short-term front-end project from an IT dispatch company, out of desperation. They said overtime would not be paid, but I signed anyway.

Last night, the manager called out in the WeChat group:
@everyone, we need to work overtime this Saturday and the remaining two Saturdays in May. Starting next week, work hours will change from 9-6 to 9-9 to rush a version delivery to the client by the end of May.

I screenshot the manager's message and sent it to the IT dispatch company's contact person.
He said: There's no overtime pay, we made that clear from the start.
I said: Then I can refuse to work overtime. Otherwise, it's mandatory overtime, which is illegal.
He said: I talked to the client, and he basically wants you to work mandatory overtime. Just bear with it. I don't make much money, and as a dispatch agent, I only get a hundred per person per month.
I said: Whether I work overtime or not is up to me. Either pay 1.5 times the overtime hours, or I'll leave on time.
He said: That won't work. 1.5 times is too much. Can we settle for five hundred?
Me: Bro, even if it's calculated at 1.5 times, it's still just over two thousand. I've cut it down to two thousand for you. Your company is somewhat well-known, you can't even come up with two thousand, can you?
Him: I'm just a messenger. Giving you five hundred is already handing over all my profit to you. That means you're making money off my share. If you want more, I'll have to talk to my boss. I've been a low-level employee at this dispatch company for three years. I know exactly how stingy the boss is. When we work overtime, we only get a 20 yuan meal allowance, nothing else.
Me: Can we settle for fifteen hundred?
Him: Really can't settle. The project only lasts three months, the profit is very small. How about eight hundred? I'm begging you, bro. I'm already losing money for you. If you mess up this deal, I'll get chewed out by the boss. And I can't find anyone to replace you. Who would hire someone for just two weeks? If you don't do a good job, we might both end up looking for new jobs.
Me: Talk to the boss again, see if you can get it to a thousand, as overtime pay for the next two weeks. That's my final offer. I haven't even counted the Saturdays yet.
Him: For the Saturday thing, you'll need to use compensatory leave. You'll have to talk to your supervisor about it. May is out of the question, I think. Let's aim for June—pick a day that's not too busy and apply for time off. If you can't get it approved, let me know, and I'll pay you overtime at the normal rate.
Me: Alright, let's leave it at that. I get it—we're all just working for a living. So that's settled. Go talk to your boss.
Him: Yeah, hang in there for me. Just get through May.

*I hung up*
*He called back*

Him: One more thing—keep it quiet. If others come asking me for money too, I'll be screwed.
Me: I know, I know. Don't worry.