I just purchased the Myst collection during the Indi sale, but when I clicked "download and install" for RealMyst (the 2014 version) from my GOG "games" page, I got an error

{
"error": "invalid_licence",
"error_description": "User #~~~~~~~~~~~~~~~~~ does not have the license for product #1207664443."
}

(I replaced the number it gave for anonymity purposes)

I have the receipt of the purchase, and other games that came in the bundle are downloading properly

In addition, when using Galaxy, it gives me an error saying that it can't connect to the GOG servers

How do I rectify this issue?

I had the same problem yesterday with Uru: Complete Collection. Bought it, it was added to my library but I just couldn't download the game files. Got the same error message. Already opened a support ticket because of this. But a few hours later it magically fixed itself and I was finally able to download the game.

So I would recommend patience. Just wait a while. There's a good chance that problem will go away by itself.

edit: Nevermind, another thread suggests it's hickups on servers...