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Registering as Relayer

Every Aura validator is an implicit relayer — fee-bearing unsigned extrinsics are included in blocks as part of normal block authorship. No special node configuration or relay service is required.

To receive fee attribution and be able to claim accumulated fees, a validator must register an EVM H160 address on-chain via pallet-relayer. This registration is restricted to active Aura validators.

Prerequisites​

Active Aura validator

The node must be running as a validator with an Aura key in the keystore. The register_relayer extrinsic is rejected for non-validators.

EVM H160 address

Any secp256k1 address the validator controls. Used exclusively for claiming fees via claim_relay_fees_to_evm.

Step 1 — Generate an EVM address​

Generate a secp256k1 key pair. Any Ethereum key derivation tool works. Using cast (Foundry):

cast wallet new

Example output:

Successfully created new keypair.
Address:     0xABCDEF...
Private key: 0xdeadbeef...

Keep the private key secure. The H160 address is what gets registered on-chain.

Key security

This address receives tokens from fee claims. Treat the private key as a hot wallet — do not reuse it across networks.

Step 2 — Submit the registration extrinsic​

Call register_relayer(evm_address) from the validator's Substrate account. This can be done via:

Polkadot.js Apps

  1. Go to Developer → Extrinsics
  2. Select the validator's account
  3. Select relayer → registerRelayer
  4. Enter the H160 address (40-char hex, without 0x)
  5. Submit and sign

ts-sdk

import { RelayerStatusModule } from '@orbinum/sdk';

// Check registration first
const statusModule = new RelayerStatusModule(api);
const isRegistered = await statusModule.isRelayer(validatorSs58);

The extrinsic writes two on-chain indexes:

  • RelayerByAccount[AccountId] → H160 — used when claiming fees to EVM
  • RelayerRegistry[H160] → AccountId — used to attribute fees from executed operations
Validator check

pallet-relayer calls T::IsValidator::contains(&who) before accepting the registration. Non-validators receive a NotValidator error.

Step 3 — Verify registration​

After the extrinsic is finalized, check registration via chain state or the SDK:

# Query via RPC
curl -sX POST http://localhost:9944 \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "state_call",
    "params": ["ShieldedPoolApi_get_merkle_tree_info", "0x"]
  }'

Or in the app — validators see the Relayer Dashboard panel in the wallet view once registered and with pending fees.

Claiming accumulated fees​

Fees accumulate in PendingRelayerFees[AccountId][asset_id] as blocks are authored. Two claim paths are available:

Private ZK note

claim_shielded_fees — call index 16

  • Requires a disclosure ZK proof
  • Funds are fully private and spendable as any note
  • Available in the Relayer Dashboard (app UI)
Direct EVM transfer

claim_relay_fees_to_evm — call index 17

  • No ZK proof required
  • Tokens go directly to the registered H160 account
  • Visible on-chain as a public transfer

See Fee Lifecycle for a full walkthrough of both paths.

Unregistering​

To stop receiving fee attribution, call unregister_relayer(). This removes both on-chain indexes. Any fees already accumulated in PendingRelayerFees remain claimable after unregistration.

pallet-relayer: relevant extrinsics​

ExtrinsicWho callsPurpose
register_relayer(evm_address)ValidatorBinds H160 → AccountId in both registry maps
unregister_relayer()ValidatorRemoves registration; stops fee attribution
set_min_relay_fee(fee)Governance (ManageOrigin)Adjusts the minimum fee required in ZK proofs

On-chain events reference​

Key events emitted by pallet-relayer:

EventMeaning
RelayerRegistered { evm_address, account }On-chain registration completed
RelayFeesConsumed { relayer, asset_id, amount }Fees deducted from pending balance (claim step)

Key events emitted by pallet-shielded-pool:

EventMeaning
ValidatorFeesClaimed { validator, asset_id, amount, ... }Fees received as private note
RelayFeesClaimedToEvm { validator, evm_address, asset_id, amount }Fees sent to H160 EVM account