Approval and refunds

First-use approval

The smart account must give the paymaster a finite native-USDC allowance 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 approval = encodePublicPaymasterApproval(1_000_000n); // 1 USDC

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

const encodedCall = await account.encodeCalls([
  {
    to: INK_PUBLIC_PAYMASTER.token.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 USDC becomes pull-based refund credit owned by the smart account.

const state = await getPublicPaymasterAccountState(publicClient, account.address);
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.