Hi
Maybe here someone from GOG support team will answer me as I've already send 2 emails via the website, 2 tweets, neither of those was answered...
My question is: how I can connect my Witcher 3 game I bought from 3party vendor to my GOG Galaxy account? I see the game in my Galaxy client, but it's not connected. Whenever I try to do this I got massage that game code has been already used. I know it's been used, but it's been used by me as I downloaded, installed and playing the game.
So how can I connect this?

I had this problem, only thing I had to do was close Galaxy and re-open it. The game should be available on the website so just download the game via the website if it is. You don't need to use Galaxy as far as I'm aware.

But I do see the game. I downloaded it from GOG website and I'm playing it. I just can't connect the game to my Galaxy client.

Yeah I did think that was the particular problem. Unfortunately nothing I can do laddy, sorry. :)

try
Library->witcher 3-> MORE->Manage->Import folder

See if the client simply does not recognise the game? I suppose that is a possibility.

Is your game listed under the library tab in Galaxy? If it is, it's "connected". If you want it on the left hand side as an installed game that is managed by the Galaxy client you either have to deinstall and reinstall the game again through the Galaxy client or you may import your game folder like mduchowski explained.

Otherwise wait for the support staff to reply. Might take a few days though and don't expect an answer on a weekend. (=

That's the thing. I can't even see the game in my library tab. It is listed on the left hand side, but not in my library.
Why is that? I do have the game, I spend the money to buy it, it's not some pirated version, so what the hell?

It's been like 5 days now and still no word from support, na answer to any of my massages to them or tweets. Support...?!

Here's a tip: stop bugging support. I say that for a very good reason. If you reply to a ticket, or comment on it, your ticket then goes to the bottom of the queue as if it was a new ticket. Just be patient, and don't expect them to answer tweets.

I contacted GOG support for having accidentally bought the wrong game, and after about 10 days they answered and solved everything. Just be patient, they'll answer :)