The code is (likely) from the Cyberpunk 2077 trailer on E3, hence the MMLXXVII being 2077 in Roman numerals.

Hidden in the same trailer they also had multiple keys for The Witcher 3 GOTY for Xbox One.

Support is probably unaware of the easter egg, hence the response you are getting contacting them.

However, I'd think the coupon might have a limited activation usage, and all things considered, it may have been for the first 2077 activations only, hence the errors people started getting some 3-4 hours ago.

We'll see how will this unfold, but I won't be surprised if the deal is gone already for those of us who missed it in the first couple of hours it went viral online. Which is a shame, was eyeing to get the STAR WARS™ Episode I: Racer if I got it to work.

I think your privacy settings forbid me from sending you a PM. Change those and I'll send you the key

Friendrequest sent and I sent you a chatmessage.

Yeah, the MMLXXVII deal doesn't work. A real shame. I got in early but couldn't go past page 67 so I figured I'd wait until GOG fixes it but they never did and instead just shut the whole thing down. Oh well, seemed to good to be true anyway

How early did you get in and when was the last it was active or showing the proper pages?

I got in nearly 7 hours ago. Seems a lot of people had difficulty getting in so no idea when it was last working

Thank you. Okay, so now we know how recent this is and that it was working 7 hours ago. So it could be possible that the server is just being slammed.

I hope it's simply a server issue but the fact that GOG hasn't acknowledged this at all has me wondering if this 'giveaway' was even supposed to happen at all :/

I definitely think it was intentional but it's possible that it was a leak or something. Maybe, something like the first 100 keys or something but right now, all we could do is speculate until one of the blues steps in and says something about it.

Absconding Zatwor + Break Into Zatwor + Fiends of Imprisonment is free on Indiegala.
https://www.indiegala.com/giveaways#giveaway

Here is my explanation "what's going on" with this "MM" code. Such codes (they all start with "MM") were given out as rewards in the old contests organized by GOG on GOG forum (Around 2014 year I think? Maybe even earlier). These codes allowed to select one game below $9.99 and they were "stuck" after 67 page.

This current code is probably just pure coincidence created by some hole in the old system.

It is a good guess, but a truly one in a million coincidence for that code to say "2077" which coincidentally is the title of the upcoming CD Projekt game. It could have been a very old easter egg from those promos you mention, considering the game was announced in 2013 with the now ancient teaser trailer.

Actually, re-watching this 2013 trailer, it has the same type of code typed in red as the new trailer, which had the Xbox One codes giveaway.

I can't exactly make out anything from the blinking text, but I didn't really try hard enough. Considering you mention these MM- starting codes from 2014 or earlier (2013?), it sounds like totally possible that this code was sitting unused for 5 years, only to be re-discovered now. The reddit thread also mentions the "teaser" trailer, so it's possible someone dug this out of the old trailer and made it viral just now. This also explains why support is unaware of it, and says there are no ongoing coupon promos.

That said, only the expiration date is odd for me, maybe it was 5+ years after issuing the code? Or it was re-activated for this E3 if no one discovered it back in 2013? The whole thing is a real mystery anyway, way to have people digging around the internet for unseen easter eggs, lol.

I've just found one such GOG's contest - its from 2011! :D

Okay, if these codes you mentioned were from 2011, I'm back at having no idea where that code came from and why it worked now for some people. Other codes starting with MM- say expired, and 2077 (and 2078 actually) is the only one saying there was an error. Usually if a code doesn't work, it would say it isn't "one of theirs", but these errors are different.

Proper mystery that one, especially with support denying the existence of any ongoing promos...