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.
UNDOCUMENTEDPOSTGetInviteHistory
https://api.steampowered.com/IPlaytestService/GetInviteHistory/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
uint32 No
UNDOCUMENTEDPOSTGetInviteOptions
https://api.steampowered.com/IPlaytestService/GetInviteOptions/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
UNDOCUMENTEDPOSTGetInvites
https://api.steampowered.com/IPlaytestService/GetInvites/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint64 No
UNDOCUMENTEDPOSTGetUserStatus
https://api.steampowered.com/IPlaytestService/GetUserStatus/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
UNDOCUMENTEDPOSTRequestInvite
https://api.steampowered.com/IPlaytestService/RequestInvite/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
fixed64 No
UNDOCUMENTEDPOSTUpdateInvites
https://api.steampowered.com/IPlaytestService/UpdateInvites/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint64[] No
int32 Noenum