Facilitator

Verification and settlement service for b402 payments

The facilitator is the off-chain service that bridges HTTP requests and blockchain settlement. It verifies payment payloads, executes on-chain transactions, and returns settlement proofs.

The facilitator never holds user funds or keys. It validates signatures, pays gas, and relays transactions.

What It Does

Capability	Description
Verify payments	Validate EIP-712 signatures against on-chain state
Settle transactions	Execute token transfers via the Relayer contract
Smart wallet ops	Build and submit ERC-4337 UserOperations
Deploy wallets	Create deterministic Nexus smart wallets
Incognito payments	Process privacy pool shield/unshield operations
Swap execution	Private token swaps with payment

Two Payment Models

EOA Payments

For standard wallets (MetaMask, private key wallets):

1. Server sends payment requirements to client
2. Client signs EIP-712 TransferWithAuthorization payload
3. Server forwards to facilitator /verify
4. Facilitator checks signature, nonce, time window, and balances
5. Server calls /settle
6. Facilitator calls transferWithAuthorization() on the Relayer contract and pays gas

Smart Wallet Payments

For ERC-7579 Nexus smart wallets:

1. Server sends payment requirements to client
2. Client calls facilitator /wallet/verify with wallet address and payment details
3. Facilitator builds unsigned UserOp with fee injection and paymaster signature
4. Client signs the UserOp hash
5. Client sends signed UserOp to /wallet/settle
6. Facilitator submits to ERC-4337 bundler
7. Bundler executes on-chain (batch: approve + transfer)

Smart wallet payments are fully gasless for the user. The paymaster covers gas costs, and the fee is deducted from the payment amount.

Official Facilitator

The hosted b402 facilitator is live at:

Base URL: https://facilitatorv3.b402.ai

Supported networks: BNB Chain mainnet, Base mainnet

Supported tokens: USDT, USDC, USD1

Rate limit: 30 requests per minute per IP

See the Facilitator API Reference for full endpoint documentation and Fee Structure for pricing details.

Interaction Flow