Hi, I bought some games, some are the main game with the addon, bought at the same time. But while installing them, I saw that at least one is missing (it's an add-on). I checked my ''purchased list'', I can see it ''bought''; but that addon is not displayed in the ''my library/all games''. I can see only the main game. So i clicked on this main game and I see a ''DLC'' link, (very small and gray, almost unvisible link) which seems connected to the addon, but the addon itself is not dispalyed.
Why is there a strange DLC link instead of a real addon? How to deal with that?

(the game is Sunless Sea with the Zubmarine addon)

Is this in Galaxy? Try closing Galaxy (right-click tray icon -> Exit) and then restarting it.
Has helped me before.

Hi, I tried... I closed the GOG Galaxy browser/manager, closed the tray icon/logged out. Re-opened it, logged in, but addon still missing. I have another game which has an ''expansion'' , I dont' know if it is considered an addon, but in that case I can see the main game and the addon (Necrovision and Necrovision Lost Company). The game Sunless Sea's addon Zubmarine is still missing (and the DLC?)...

In Galaxy click More -> Settings. Does the DLC perchance show up there (checkbox?).

Otherwise it's strange... I would try to contact support on this. Although they're a skeleton crew over the weekend, so you probably won't hear back until Monday.

You could try restarting the computer and/or removing and re-installing the game.

In the meantime you could try downloading it using web browser.
https://www.gog.com/forum/sunless_sea/zubmariner_zubmerging_doesnt_work/post3

I checked... In Galaxy browser, I selected the game, clicked More, the DLC checkbox is flagged (and it shows the title addon Zubmarine). Nothing else.

I read the link you guys posted, another user said that in this case it requires a '' DLC installer, separately ,from gog library and install it the old fashioned way'' because it seems ''there is no option to install it with gog galaxy''.

So I logged in the site, but I can't figure it out how to download it... It's not even in my site account library/my collection
(i can only see it in my ''orders/purchases'')...

DLCs are not not separate entries, they're kept together with games. You should find Zubmarine installer under Sunless Sea.

Edit: Added a screenshot with the only DLC among my games I probably have.