isNonceUsed - Palindrome Crypto Pay SDK Documentation

async isNonceUsed(
  escrowId: bigint,
  signer: Address,
  nonce: bigint
): Promise<boolean>

Checks whether a specific nonce has already been used by a signer for a particular escrow. Useful for verifying signature validity before submission.

Parameters

escrowId: bigint – The escrow ID
signer: Address – The signer's wallet address
nonce: bigint – The nonce to check

Returns

Promise<boolean> – true if nonce is used, false if available

import { createPalindromeSDK } from '@/lib/createSDK';

const { sdk, walletClient } = await connectAndInitSDK();

const escrowId = 42n;
const signer = walletClient.account.address;

// Check if nonce 0 is used
const nonce0Used = await sdk.isNonceUsed(escrowId, signer, 0n);
console.log("Nonce 0 used:", nonce0Used);

// Check if nonce 5 is used
const nonce5Used = await sdk.isNonceUsed(escrowId, signer, 5n);
console.log("Nonce 5 used:", nonce5Used);

Validation Before Submission

async function submitSignedTransaction(
  escrowId: bigint,
  signature: Hex,
  deadline: bigint,
  nonce: bigint,
  signer: Address
) {
  // Verify nonce is still valid
  const isUsed = await sdk.isNonceUsed(escrowId, signer, nonce);

  if (isUsed) {
    throw new Error("Nonce already used — signature is invalid");
  }

  // Proceed with submission
  return await sdk.confirmDeliverySigned(...);
}

Relayer Validation

// Backend: Validate incoming signature request
app.post('/api/relay', async (req, res) => {
  const { escrowId, signature, deadline, nonce, signer } = req.body;

  // Check nonce hasn't been used
  const isUsed = await sdk.isNonceUsed(BigInt(escrowId), signer, BigInt(nonce));
  if (isUsed) {
    return res.status(400).json({ error: "Nonce already used" });
  }

  // Check deadline hasn't expired
  if (sdk.isSignatureDeadlineExpired(BigInt(deadline))) {
    return res.status(400).json({ error: "Signature expired" });
  }

  // Submit transaction
  const txHash = await sdk.startDisputeSigned(...);
  res.json({ success: true, txHash });
});

See also → getUserNonce() · getNonceBitmap()