I don't know what's going on with this game/gog but I've been unable to install the game. Lutris complains of a 404 error. Figured it's a lutris issue so I tried to download directly from the site and nope, get an XML error complaining about a missing key. What the hell is going on? I tried contacting support to find out why the game I bought wasn't downloading and my issue was marked solved as soon as I made it and I've heard absolutely nothing back. Two weeks later and this game is STILL uninstallable.

I've been getting the same error message as well, and I've been unable to download the offline installers. I've contacted GOG twice about it, but nothing was done. I combed through my entire library to see if some offline installers were still affected by the server outage about a week or two ago. Literally every other game (out of 602) was working except this one. I'll try to inquire about it, again.
[Update: 2023/09/22]

The offline installers are finally available again. Thanks GOG staff.