All successful responses are returned with TXN (Transaction Successful). TUP (Transaction Under Process) should be considered as Pending. In case of failure, the Instantpay API returns a JSON error response with parameters that detail the reason for the failure.

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"TXN" => "Transaction Successful",
"TUP" => "Transaction Under Process",
"IRA" => "Invalid Refill Amount",
"RBT" => "Refill Barred Temporarily",
"IAN" => "Invalid Account Number",
"IAB" => "Insufficient Wallet Balance",
"DTX" => "Duplicate Transaction",
"ISE" => "System Error",
"IAT" => "Invalid Access Token",
"SPD" => "Service Provider Downtime",
"SPE" => "Service Provider Error",
"ITI" => "Invalid Transaction ID",
"DTB" => "Denomination Temporarily Barred",
"TSU" => "Transaction Status Unavailable",
"ISP" => "Invalid Service Provider",
"RPI" => "Request Parameters are Invalid or Incomplete",
"AAB" => "Account Blocked, Contact Helpdesk",
"ANF" => "Account not found",
"UED" => "Unknown Error Description, Contact Helpdesk",
"IEC" => "Invalid or Unknown Error Code",
"IRT" => "Invalid Response Type",
"IPE" => "Internal Processing Error",
"IAC" => "Invalid Dealer Credentials",
"UAD" => "User Access Denied",
"TRP" => "Transaction Refund Processed",
"TDE" => "Transaction Dispute Error, Contact Helpdesk",
"DLS" => "Dispute Logged Successfully",
"DID" => "Duplicate Agent Transaction ID",
"OUI" => "Outlet Unauthorized or Inactive",
"ODI" => "Outlet Data Incorrect",
"RNF" => "Remitter Not Found",
"RAR" => "Remitter Already Registered",
"UAR" => "User Already Registered",
"IVC" => "Invalid Verification Code or OTP",
"IUA" => "Invalid User Account - Outlet",
"SNA" => "Service not available",
"ERR" => "Provider Failure",
"FAB" => "Failure at Bank end",
"UFC" => "Fare has been changed",
"OTP" => "OTP Successfully sent",
"EOP" => "OTP Expired",
"OLR" => "OTP limit reached",
"ONV" => "OTP not valid",
"RAB" => "Remitter Blocked",
"VCI" => "Version Compatablity Iussue",
"OUE" => "Unknown Method",
"KYC" => "KYC is mandatory to avail this service",
"USM" => "Under Scheduled Maintenance",
"CNL" => "Currently Not Live",

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Note:

Any other error codes except given above are to be confirmed before taking any action and should be treated as pending.

There is one case of Timeout if you received timeout please treat that Transaction in Pending and Check the Status of the Transaction from Transaction Status API and take action accordingly to that status.