Approval and refunds

First-use approval

The smart account must give the paymaster a finite allowance for its selected reimbursement token before it can use prepaid gas. The public paymaster cannot sponsor its own approval because reimbursement is not yet available.

The SDK encodes the inner ERC-20 call:

const selectedToken = INK_PAYMENT_TOKENS.USDG;
const approval = encodePublicPaymasterApproval(1_000_000n); // 1 token at six decimals

Your smart account then wraps that call using its own execution format. With a Viem smart account:

const encodedCall = await account.encodeCalls([
  {
    to: selectedToken.address,
    value: 0n,
    data: encodePublicPaymasterApproval(1_000_000n),
  },
]);

Submit encodedCall using an owner-paid operation or another gas mechanism. The complete type-checked example in sdk/examples/encode-approval.ts creates a Viem Bundler Client without a paymaster, sends the approval, and waits for its receipt.

Prefer a finite allowance sized for expected usage rather than an unlimited approval. Monitor it with getPublicPaymasterAccountState and replenish it through your normal owner-paid path.

Refund credit

The paymaster precharges the quoted maximum during validation. After execution, unused precharge becomes pull-based refund credit in the selected token, owned by the smart account.

const state = await getPublicPaymasterAccountState(
  publicClient,
  account.address,
  INK_PUBLIC_PAYMASTER,
  selectedToken.symbol,
);
console.log(state.refundCredit);

To claim it, encode the paymaster call and have the smart account execute it:

const claim = encodePublicPaymasterRefundClaim(recipient);
const encodedCall = await account.encodeCalls([
  {to: INK_PUBLIC_PAYMASTER.paymaster, value: 0n, data: claim},
]);

The account that owns the credit must make the call. The recipient may be a different address.