This page is just a reference of all the known Steam APIs, I do not know how they work. Please do not email me with questions.
PUBLISHERPOSTAssociateWorkshopItems
https://partner.steam-api.com/ISteamWorkshop/AssociateWorkshopItems/v1/
NameValueTypeRequiredDescription
uint32 Yes AppID of game this transaction is for
uint32 Yes Number of items to associate
uint64[] Nothe workshop published file id
uint32[] No3rd party ID for item
float[] NoPercentage of revenue the owners of the workshop item will get from the sale of the item [0.0, 100.0]. For bundle-like items, send over an entry for each item in the bundle (gameitemid = bundle id) with different publishedfileids and with the revenue percentage pre-split amongst the items in the bundle (i.e. 30% / 10 items in the bundle)
string[] NoGame's description of the game item
PUBLISHERPOSTGetContributors
https://partner.steam-api.com/ISteamWorkshop/GetContributors/v1/
NameValueTypeRequiredDescription
uint32 Yes AppID of game this transaction is for