Fee Payment

Normative rules for implementations of FeePaymentMethod and for wallets assembling fee-paid transactions.

FeePaymentMethod Contract

FEE-1. FeePaymentMethod::get_asset MUST return the address of the Aztec asset that will be debited to pay the fee. For Fee-Juice-based methods, this MUST equal protocol_contract_address::fee_juice().

FEE-2. FeePaymentMethod::get_fee_payer MUST return the account address that will be debited, which MAY differ from the transaction’s from.

FEE-3. FeePaymentMethod::get_fee_execution_payload MUST return an ExecutionPayload that, when merged with the user’s payload, is sufficient to satisfy the network’s fee-payment constraints for the resulting transaction — no additional calls SHOULD be required.

FEE-4. A FeePaymentMethod instance MUST produce deterministic output for a given input state; repeat calls across the same chain head MUST yield equivalent payloads.

Binding to a Transaction

FEE-5. A fee-execution payload MUST NOT be reused across unrelated transactions. A wallet MUST recompute the payload for each distinct TxExecutionRequest.

FEE-6. GasSettings submitted alongside a fee payment MUST include a max_fee_per_gas no lower than the simulation estimate at the time of submission. Wallets SHOULD budget a margin; callers MAY choose the margin.

Native Payment

FEE-7. NativeFeePaymentMethod::new(payer) produces a payment from payer’s Fee Juice balance. Simulation MUST verify the payer holds sufficient balance at the chain head; inclusion-time failure is a correctness concern and SHOULD surface via a simulation error.

Sponsored Payment

FEE-8. SponsoredFeePaymentMethod MAY be refused by the sponsor contract at inclusion. Applications consuming sponsored payment MUST surface inclusion-time revert to the user with the sponsor’s reason.

Claim-Based Payment

FEE-9. FeeJuicePaymentMethodWithClaim MUST verify the referenced L1 deposit is consumable on L2 before proving the transaction; consumption of an unready claim is a correctness bug.

FEE-10. A claim message MUST be consumed at most once. The network enforces this via the nullifier tree; implementations MUST NOT attempt to replay a successful claim tx.

Meta Payment

FEE-11. AccountEntrypointMetaPaymentMethod wraps the fee call through the account’s own entrypoint; it MUST be used only when the account entrypoint supports fee-carrying calls, and MUST produce the same asset/payer guarantees as the underlying strategy it wraps.

Custom FeePaymentMethod Implementations

FEE-12. A custom implementation MUST satisfy FEE-1 through FEE-5. Implementations serving private FPC flows or other patterns MUST document any additional guarantees they provide.