This is nothing to do with Steam Downloader and the API, and everything to do with the publisher of the game not enabling those who don't own the game on Steam to download workshop mods.

The API Steam downloader (and similar web pages and tools) uses is a web-based API - it never had anything to do with the game itself.

If you want a mod that's currently "locked" for you because you don't have it on Steam, your options are:

1) Contact the publisher of the game and get them to unlock it (this sometimes works - Klei unlocked Invisible Inc workshop mods for example).
2) See if the mod is available elsewhere, such as Moddb or NexusMods - if not, contact the developer of the mod and get them to get their shit together.
3) Buy the game on Steam.

I suspect that Steam "locks" the workshop by default, which is why newer games tend to often not be accessible via the downloader - meaning it's up to the game's publisher to explicitly set the workshop to be available.

If I would have known this earlier, I would never had bought this game over GOG but over Steam.
Also, the connecting to other people is a big problem.

Do someone know if one can get a refund for a transfer to Steam from the Publisher?

But I learnt my lesson, I will only buy singleplayer games or games with internal multiplayer management on GOG, but never ever games that:
- need a infrastructure for mods
- have their multiplayer outsourced to the distribution platform

Hello everyone.

Considering that this thread is still relatively active.. and a top result on google as well..

The website www.steamworkshopdownloader.io has now officially been updated to support many more games.

Any game that doesn't explicitly disable 'anonymous game server downloads' should be working now.

If your game still doesn't work, see if you can get the game developer to enable this setting.

Enjoy!

-

The technicalities:

We are no longer just relying on the outdated "Steam Web API" (also known as the ISteamRemoteStorage interface) to retrieve files. Most download tools rely on this.

Using a large pool of steam clients, we were able to automate file retrieval of games that use the newer "User Generated Content API" (also known as the ISteamUGC interface). So many more modern games are supported by our website.

(so please be aware of any website that claims "not to be allowed to download files"- it may actually just be lacking support for the newer API)

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In FFXV mods works great, when I use ModOrganizer, but fbx files with texture - hard to find (easy only nude).

But when I dowlnoad:

https://steamcommunity.com/workshop/filedetails/?id=1412117008 using

http://steamworkshop.download/download/view/1412117008

and open rar files finally get:

Cindy_1.ffxvbinmod
636702736398148492.dat
636653595706376301.dat
636653581151674265.dat
636651281233827512.dat
636647689220241983.dat
636646118577730000.dat

What to do with this files?

Working Steam Workshop downloader on Github:

github.com/shadoxxhd/steamworkshopdownloader/releases

Downloading workshop files only works if you also own the game on Steam.
One more reason for me not to buy anything there, even if many MODs are then not available.

If someone stumbles upon this topic later on and will still not know how to download steam mods for himself to use in games then use this website:

steamworkshopdownloader.io

you paste steam workshop link it will automatically generate you a copy paste command for your steamcmd.exe (you dont need to login you can use login anonymous)
there is a tutorial on a website
you can also paste whole collections that way and download all of them one by one