Sign for a fee sponsor

A fee sponsor pays the fee for a transaction that someone else sends. On Tempo, the sender signs first and the sponsor signs the same transaction afterwards. signTempoTransaction from @dynamic-labs-sdk/tempo/waas produces the sender’s half: it signs with an embedded Tempo wallet and returns the signed transaction without broadcasting it.

The SDK signs for the sender only. Your app provides the sponsor that adds its signature and broadcasts the transaction. This guide covers the sender’s side.

Sign a transaction that awaits a fee payer

Set awaitingFeePayer to true. The wallet signs the transaction as one whose fee a sponsor will pay, and the function returns the serialized signed transaction in signedTransaction.

import type { TempoWalletAccount } from '@dynamic-labs-sdk/tempo';
import { signTempoTransaction } from '@dynamic-labs-sdk/tempo/waas';
import { encodeFunctionData, erc20Abi, parseUnits } from 'viem';

const signForSponsor = async (walletAccount: TempoWalletAccount) => {
  const { signedTransaction } = await signTempoTransaction({
    awaitingFeePayer: true,
    calls: [
      {
        data: encodeFunctionData({
          abi: erc20Abi,
          args: ['0xRecipientAddress...', parseUnits('1.5', 6)],
          functionName: 'transfer',
        }),
        to: '0xTip20TokenAddress...',
      },
    ],
    walletAccount,
  });

  return signedTransaction;
};

Send signedTransaction to your sponsor service. It is a signed Tempo transaction that still needs the fee payer’s signature, so it cannot be broadcast as it is.

Parameters

signTempoTransaction accepts the same Tempo fields as sendTempoTransaction, plus awaitingFeePayer.

Parameter	Type	Description
`walletAccount`	`WalletAccount`	The embedded Tempo wallet that signs.
`awaitingFeePayer`	`true` (optional)	Leaves the fee to a sponsor who signs afterwards. Cannot be combined with `feeToken`.
`calls`	`readonly TempoTransactionCall[]`	The calls the transaction executes atomically. Each call takes `to`, `data`, and `value`.
`feeToken`	`Hex` (optional)	The TIP-20 token address that pays the fee. Leave it out when `awaitingFeePayer` is set.
`gas`	`bigint` (optional)	The gas limit. Defaults to a buffered estimate, and the SDK uses the larger of your value and its estimate.
`nonceKey`	`bigint` (optional)	Selects a parallel nonce lane. See Use parallel nonce lanes.
`validAfter`	`number` (optional)	A Unix timestamp in seconds. The transaction is not valid before this time.
`validBefore`	`number` (optional)	A Unix timestamp in seconds. The transaction expires after this time. See Set a validity window.

Leave awaitingFeePayer out and signTempoTransaction returns a signed transaction that the sender pays for, which you can broadcast yourself.

Returns

Promise<{ signedTransaction: string }>. The value is the serialized signed transaction. Nothing is sent to the network.

Rules

The sponsor chooses the fee token, so a transaction that awaits a fee payer cannot name one. Passing awaitingFeePayer together with feeToken throws TempoTransactionValidationError before the wallet signs, and so does an awaitingFeePayer value other than true. A transaction that awaits a fee payer cannot be broadcast by the sender. sendTempoTransaction throws TempoTransactionValidationError when awaitingFeePayer is set, and so does the viem sendTransaction of the Tempo wallet client. Use signTempoTransaction for these transactions.

Set validBefore on a transaction you hand to a sponsor. If the sponsor does not sign and broadcast it in time, it expires instead of staying valid indefinitely.

Errors

Error	When it is thrown
`InvalidParamError`	The wallet account is not an embedded Tempo wallet account.
`TempoTransactionValidationError`	A field is malformed or inconsistent, for example `awaitingFeePayer` combined with `feeToken`.

Pay fees with a TIP-20 token covers the case where the sender pays the fee.
Tempo covers setup, transfers, and sendTempoTransaction.

​Sign a transaction that awaits a fee payer

​Parameters

​Returns

​Rules

​Errors

​Related

Sign a transaction that awaits a fee payer

Parameters

Returns

Rules

Errors

Related