This isn't a first time buyer, though. My client already used Fiverr and isn't new to this platform. And besides, it doesn't really matter.
The point is that if you start working on milestones in advance, which many sellers will do, it leaves you totally vulnerable in case your buyer decides to ghost you.
I just spoke with Customer Support and they pretty much told me that system is working as intended, which just makes the whole situation more ridiculous.
I completed 1000$ worth of work that I currently have no way to charge. I'm going to avoid milestones like a plague from now on.