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.

Creates a lobby and sets its related lobby data

https://partner.steam-api.com/ILobbyMatchmakingService/CreateLobby/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 Yes
int32 Yes
int32 Yes
string Yes
uint64 Yes
{message} Yes

Returns lobby data and member list

https://partner.steam-api.com/ILobbyMatchmakingService/GetLobbyData/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 Yes
uint64 Yes

Removes a user from a lobby

https://partner.steam-api.com/ILobbyMatchmakingService/RemoveUserFromLobby/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 Yes
uint64 Yes
uint64 Yes