Errors

/verify returns invalidReason. /settle returns errorReason. A paid resource usually copies that string into the next 402 error field.

Client / payload

`unsupported_x402_version`	Set `x402Version` to 2.
`unsupported_scheme`	Only `exact` is implemented.
`wrong_network`	Use `cosmos:gonka-mainnet`.
`missing_signed_tx`	`payload.signedTx` is empty.
`invalid_signed_tx`	Not valid base64 or not a protobuf `TxRaw`.
`authorization_expired`	`timeoutAt` is in the past. Sign again.
`payer_mismatch`	`authorization.from` does not match the tx signer.
`recipient_mismatch`	Tx recipient is not `payTo`.
`asset_mismatch`	Wrong denom or CW-20 contract.
`invalid_amount`	Requirements amount is missing or not a positive integer string.
`insufficient_amount`	Tx pays less than `accepted.amount`.
`invalid_signature`	SignDoc does not match the signature / pubkey / chain id / account number.

Chain state

`account_lookup_failed`	LCD could not load the payer account. The address may never have been funded.
`stale_sequence`	Signed sequence is not the current one. Re-query and re-sign. Do not reuse the payload.
`balance_lookup_failed`	Bank or CW-20 query failed during verify.
`insufficient_funds`	Verify-time balance is below the tx amount.
`replayed_payment`	This exact `TxRaw` was already settled. New payment needs a new sequence.
`settlement_pending`	Broadcast succeeded; inclusion was not seen before timeout. Inspect `transaction` on gonka.gg before paying again.

Broadcast

If the chain rejects the tx, errorReason is the LCD error (HTTP status, broadcast code N, or the raw log). Typical causes: sequence already used, memo/message decode issues, or the account cannot pay. Fix the tx and sign a new one.

HTTP 402 from /demo

`PAYMENT-SIGNATURE header is required`	First request, or the header was omitted.
`invalid PAYMENT-SIGNATURE`	Header is not base64 JSON.