Sounds very fishy, where is the game that they're providing an upfront payment for?

You keep saying you're not trying to scam, but you wont show anyone the game link on steam because you don't have "time". I will be more than happy to revert my statement if found wrong, but this seems very off.

Again, I don't know GOG, but common sense would tell me they wouldn't give you an up front payment with the 40% option until fulfilled unless your game has prior success selling on Steam, or another platform. If your game is making money on other platforms, why would you sell the IP off for short term cash when GOG has a deal for you and you can potentially make more money? Doesn't make sense, and I'm calling you out on it.

I cannot email them because I don't know the game, and who you are as a developer. What is your company?

Yeah, no -- this is way too suspicious and almost certainly a scam -- I'm removing the post contents and closing this topic.