Fee Sponsoring

Enable gasless transactions by routing submissions through a relayer proxy.

Overview

By default, Smart Account Kit submits transactions directly via the Stellar RPC. Configure a relayerUrl to route submissions through a relayer proxy that sponsors fees - making your app effectively gasless for end users.

Setup

const kit = new SmartAccountKit({
  rpcUrl: 'https://soroban-testnet.stellar.org',
  networkPassphrase: 'Test SDF Network ; September 2015',
  accountWasmHash: 'YOUR_WASM_HASH',
  webauthnVerifierAddress: 'YOUR_VERIFIER',
  relayerUrl: 'https://my-relayer.example.com',  // ← add this
});

Once configured, all transfer(), signAndSubmit(), and executeAndSubmit() calls automatically route through the relayer.

Bypassing the Relayer

To use RPC directly for a specific operation:

// Force RPC for this transfer only
await kit.transfer(tokenContract, recipient, amount, { forceMethod: 'rpc' });

Relayer Protocol

The relayer proxy must accept POST requests with one of two formats:

For invokeHostFunction flows (func + auth):

{ "func": "<xdr>", "auth": ["<xdr>", ...] }

For signed transactions (e.g. deployments):

{ "xdr": "<signed_tx_xdr>" }

The relayer wraps the transaction in a fee bump, sponsors fees, and returns the submitted transaction hash.

Using RelayerClient Directly

Access the relayer client directly via kit.relayer:

if (kit.relayer) {
  // Submit func + auth for fee sponsoring
  const result = await kit.relayer.send(funcXdr, authXdrs);

  // Or submit a signed transaction
  const result = await kit.relayer.sendXdr(signedTx);

  if (result.success) {
    console.log('Hash:', result.hash);
  } else {
    console.error('Error:', result.error, result.errorCode);
  }
}

See RelayerClient for the full API reference.