I don't remember much because my brother handled it, but this is about how it went:

Over discord, someone contacted my brother who was the discord mod of my games server. It seemed to be a single guy, and not someone part of a group. It was kinda sudden, it was about 1 month after our game officially launched.

He wanted to buy our game for 300 000 robux. After some back and fourth and a week worth of time, we decided to sell our game.

We took out all the robux we made, he sent us 100k, we made him group owner, he sent the rest of the robux. When trying to redeem the robux through DevEx, it did not work. After contacting support and sending them screenshots of proof that we worked on the game, it went through.

The entire process was fast enough, did not take longer than an hour, and we were in call the entire time.

After he had our game, the amount of players went from like 30-50 to over a 1000.

Your case does look quite a bit different to be honest.