Leave blank for normal behavior. With a value, the real POST is skipped and this is sent straight back to the SDK as the readyremit-transfer-failed error payload. Any error code works, not just the examples below — whatever code the SDK branches on (QuoteAmountChanged, TransferDuplicatedByQuote, NetworkError, RspTransferException…). Applies to both the transfer and RTAF funding flows, and honors Transfer Wait Time above.
Error body: { "code": "SourceAccountFundsNotAvailable", "message": "Source account funds are not available." }
Array of errors: [{ "code": "CustomerApiError", "message": "Transfer services are temporarily unavailable." }]
A captured axios error (anything with a response key) also works — its response.data is what reaches the SDK. Only code and message cross the iframe boundary; the SDK formats every forced error as a 500.