Gasless Transactions

Participants don't need Sepolia ETH. Registering a profile, submitting a quiz score, posting to the Feed and voting are all paid for by the gas station, the admin wallet configured with ADMIN_PRIVATE_KEY / ADMIN_ADDRESS.

How it works

The portal uses ERC-2771 meta-transactions:

1. The participant clicks Register, Submit or a vote button. MetaMask asks them to sign a message (EIP-712 typed data). No transaction, no gas.
2. The portal sends the signed request to POST /api/relay.
3. The gas station checks it, simulates it, and submits it to GaslessForwarder.sol from the admin wallet, paying the gas.
4. The forwarder verifies the signature on-chain and calls the target contract with the participant's address appended to the calldata.
5. ProfileRegistry, QuizScoresV2 and FeedContract trust the forwarder and read the participant through _msgSender(). On-chain, the profile, score, post or vote belongs to the participant's wallet, not the gas station's.

Participant ──sign──▶ /api/relay ──tx (admin pays gas)──▶ GaslessForwarder ──call + from──▶ Registry / Quiz / Feed

Security properties

• The gas station can't act on anyone's behalf. Every request carries the participant's EIP-712 signature, which the forwarder checks on-chain.
• No replays. Each request has a random nonce that is marked used on execution, and a deadline (1 hour).
• The gas station only pays for portal actions. /api/relay only relays register, submitScore, submit and vote on the configured contracts, and simulates every request first, so failing requests (Already registered, Already submitted to this topic, ...) cost nothing.
• Quiz scores still need the admin's score signature. Gasless submission doesn't change how scores are authorized.
• Spending guards. The relay refuses to send when gas costs more than GAS_STATION_MAX_FEE_GWEI (default 50) or the station holds less than GAS_STATION_MIN_BALANCE_ETH (default 0.005).

Fallback

The portal falls back to a regular wallet transaction (participant pays gas) when:

• VITE_FORWARDER_ADDRESS isn't set,
• the target contract doesn't trust the forwarder (for example the legacy v1 contracts), or
• the gas station is unavailable (not configured, out of funds, gas too expensive).

Shipping the code before the new contracts are deployed is safe: everything keeps working as before.

Rollout

The existing contracts read msg.sender directly, so they have to be redeployed with forwarder support. Deploy with Remix on Sepolia (Injected Provider - MetaMask).

1. Deploy the forwarder

Deploy GaslessForwarder.sol (no constructor arguments). It has no owner and no admin functions.

2. Deploy and migrate the registry

1. Deploy ProfileRegistry.sol with (forwarderAddress).
2. Copy the profiles from the current registry (0x2EE14624EF2d9c2ED151bDC2fF6Bab724bf4830D) in batches of 50: migrateFromRegistry(0x2EE1…830D, 0, 50), then (…, 50, 50), (…, 100, 50), … until you pass its getProfileCount().
3. Compare getProfileCount() on both registries, then call finalizeMigration().

warning

Anyone who registers on the old registry after its batch has run won't be carried over. Do this at a quiet time, and re-run migrateFromRegistry with a later start offset if needed before finalizing.

3. Deploy the quiz and feed contracts

• QuizScoresV2.sol with (adminAddress, newRegistryAddress, forwarderAddress). Update the active event's contract in src/config/events.js.
• FeedContract.sol with (newRegistryAddress, forwarderAddress). Posts on the previous feed contract aren't carried over.

4. Configure Vercel

Variable	Value
VITE_FORWARDER_ADDRESS	GaslessForwarder address
VITE_PROFILE_REGISTRY_ADDRESS	New ProfileRegistry address
VITE_CONTRACT_ADDRESS	New QuizScoresV2 address
VITE_FEED_CONTRACT_ADDRESS	New FeedContract address
ADMIN_PRIVATE_KEY / ADMIN_ADDRESS	Gas station wallet (already set)
GAS_STATION_MAX_FEE_GWEI	Optional, default 50
GAS_STATION_MIN_BALANCE_ETH	Optional, default 0.005

Redeploy so the new VITE_ values are bundled.

5. Keep the station funded

Top up the admin wallet with Sepolia ETH. Each action costs the station roughly one transaction: about 100k gas for a vote, 190k for a registration, 210k for a quiz score and 240–260k for a feed post. At 1 gwei that is 0.0001–0.00026 ETH per action. Failed relays and low balances are logged in the Vercel function logs as relay error and Gas station balance low.