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.
PUBLISHERPOSTAdjustAgreement
https://partner.steam-api.com/ISteamMicroTxnSandbox/AdjustAgreement/v1/
NameValueTypeRequiredDescription
uint64 Yes SteamID of user with the agreement
uint64 Yes ID of agreement
uint32 Yes AppID of game
string Yes Date for next process
PUBLISHERPOSTCancelAgreement
https://partner.steam-api.com/ISteamMicroTxnSandbox/CancelAgreement/v1/
NameValueTypeRequiredDescription
uint64 Yes SteamID of user with the agreement
uint64 Yes ID of agreement
uint32 Yes AppID of game
PUBLISHERPOSTFinalizeTxnv2
https://partner.steam-api.com/ISteamMicroTxnSandbox/FinalizeTxn/v2/
NameValueTypeRequiredDescription
uint64 Yes 3rd party ID for transaction
uint32 Yes AppID of game this transaction is for
PUBLISHERGETGetReportv5
https://partner.steam-api.com/ISteamMicroTxnSandbox/GetReport/v5/
NameValueTypeRequiredDescription
uint32 Yes AppID of game this transaction is for
string NoReport type (GAMESALES, STEAMSTORE, SETTLEMENT)
string Yes Beginning time to start report from (RFC 3339 UTC format)
uint32 NoMax number of results to return (up to 1000)
PUBLISHERGETGetUserAgreementInfov2
https://partner.steam-api.com/ISteamMicroTxnSandbox/GetUserAgreementInfo/v2/
NameValueTypeRequiredDescription
uint64 Yes SteamID of user making purchase
uint32 Yes AppID of game
PUBLISHERGETGetUserInfov2
https://partner.steam-api.com/ISteamMicroTxnSandbox/GetUserInfo/v2/
NameValueTypeRequiredDescription
uint64 NoSteamID of user making purchase
string Noip address of user in string format (xxx.xxx.xxx.xxx). Only required if usersession=web
uint32 NoAppID of game this transaction is for
PUBLISHERPOSTInitTxnv3
https://partner.steam-api.com/ISteamMicroTxnSandbox/InitTxn/v3/
NameValueTypeRequiredDescription
uint64 Yes 3rd party ID for transaction
uint64 Yes SteamID of user making purchase
uint32 Yes AppID of game this transaction is for
uint32 Yes Number of items in cart
string Yes ISO 639-1 language code of description
string Yes ISO 4217 currency code
uint32[] Yes 3rd party ID for item
uint32[] Yes Quantity of this item
int32[] Yes Total cost (in cents) of item(s)
string[] Yes Description of item
string[] NoOptional category grouping for item
string[] NoOptional recurring billing type
string[] NoOptional start date for recurring billing
string[] NoOptional end date for recurring billing
string[] NoOptional period for recurring billing
uint32[] NoOptional frequency for recurring billing
string[] NoOptional recurring billing amount
PUBLISHERPOSTProcessAgreement
https://partner.steam-api.com/ISteamMicroTxnSandbox/ProcessAgreement/v1/
NameValueTypeRequiredDescription
uint64 Yes SteamID of user with the agreement
uint64 Yes ID of agreement
uint32 Yes AppID of game
int32 Yes Total cost (in cents) to charge
string Yes ISO 4217 currency code
PUBLISHERGETQueryTxnv3
https://partner.steam-api.com/ISteamMicroTxnSandbox/QueryTxn/v3/
NameValueTypeRequiredDescription
uint32 Yes AppID of game this transaction is for
uint64 No3rd party ID for transaction
uint64 NoSteam transaction ID
PUBLISHERPOSTRefundTxnv2
https://partner.steam-api.com/ISteamMicroTxnSandbox/RefundTxn/v2/
NameValueTypeRequiredDescription
uint64 Yes 3rd party ID for transaction
uint32 Yes AppID of game this transaction is for