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.
UNDOCUMENTEDCheckInventoryAvailableByPackage
https://api.steampowered.com/IPhysicalGoodsService/CheckInventoryAvailableByPackage/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
int32 No
string No