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.
UNDOCUMENTEDPOSTAddItemsToCart
https://api.steampowered.com/IAccountCartService/AddItemsToCart/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
string No
CAccountCart_AddItemsToCart_Request_ItemToAdd No
CUserInterface_NavData No
string No
string No
string No
string No
string No
uint32 No
string No
uint64 No
bool No
CUserInterface_CuratorData No
uint32 No
uint64 No
bool No
bool No
CAccountCart_AddItemsToCart_Request_ItemToAdd[] No
uint32 No
uint32 No
CartGiftInfo No
int32 No
CartGiftMessage No
string No
string No
string No
string No
int32 No
AccountCartLineItemFlags No
bool No
bool No
UNDOCUMENTEDPOSTDeleteCart
https://api.steampowered.com/IAccountCartService/DeleteCart/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
UNDOCUMENTEDGetCart
https://api.steampowered.com/IAccountCartService/GetCart/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
string No
UNDOCUMENTEDPOSTGetRelevantCoupons
https://api.steampowered.com/IAccountCartService/GetRelevantCoupons/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
https://api.steampowered.com/IAccountCartService/MergeShoppingCartContents/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
fixed64 No
string No
UNDOCUMENTEDPOSTModifyLineItem
https://api.steampowered.com/IAccountCartService/ModifyLineItem/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint64 No
string No
CartGiftInfo No
int32 No
CartGiftMessage No
string No
string No
string No
string No
int32 No
AccountCartLineItemFlags No
bool No
bool No
uint64 No
UNDOCUMENTEDPOSTRemoveItemFromCart
https://api.steampowered.com/IAccountCartService/RemoveItemFromCart/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint64 No
string No