On-Chain Verification

const provider = new RpcProvider({
  nodeUrl: "https://starknet-mainnet.infura.io/v3/YOUR_KEY",
});

const receipt = await provider.getTransactionReceipt(txHash);

if (receipt.execution_status !== "SUCCEEDED") {
  throw new Error(`Transaction failed: ${receipt.execution_status}`);
}

// Transfer event key = starknet_keccak("Transfer")
const TRANSFER_KEY =
  "0x99cd8bde557814842a3121e8ddfd433a539b8c9f14bf31ebf108d12e6196e9";

const USDC_ADDRESS =
  "0x033068f6539f8e6e6b131e6b2b814e6c34a5224bc66947c47dab9dfee93b35fb";

const transferEvent = receipt.events.find((event) => {
  const isUsdc = BigInt(event.from_address) === BigInt(USDC_ADDRESS);
  const isTransfer = event.keys[0] === TRANSFER_KEY;
  return isUsdc && isTransfer;
});

if (!transferEvent) {
  throw new Error("No USDC Transfer event found — transfer failed silently");
}

// StarkNet Transfer events use indexed parameters (keys):
// keys[0] = Transfer selector
// keys[1] = from address
// keys[2] = to address
// data[0] = amount (low 128 bits)
// data[1] = amount (high 128 bits)
const from = transferEvent.keys[1];
const to = transferEvent.keys[2];
const amountLow = BigInt(transferEvent.data[0]);
const amountHigh = BigInt(transferEvent.data[1]);
const amount = amountLow + (amountHigh << 128n);

console.log(`Verified: ${amount} units from ${from} to ${to}`);

const balanceBefore = await getBalance(provider, tokenAddress, recipientAddress);

const txHash = await serverClient.transfer({ params: { ... } });

// Wait for the tx to be included in a block
await provider.waitForTransaction(txHash);

const balanceAfter = await getBalance(provider, tokenAddress, recipientAddress);

if (balanceAfter <= balanceBefore) {
  throw new Error("Balance did not increase — transfer may have failed");
}

async function getBalance(provider, token, account) {
  const result = await provider.callContract({
    contractAddress: token,
    entrypoint: "balance_of",
    calldata: [account],
  });
  return BigInt(result[0]) + (BigInt(result[1]) << 128n);
}

// This tells you the tx is on-chain, NOT that tokens moved
const status = await serverClient.getTransactionStatus({ hash: txHash });
// status.onChainStatus: "ACCEPTED_ON_L2" | "ACCEPTED_ON_L1" | "REJECTED" | ...