Facilitator

The Ultravioleta Facilitator (x402-rs) is a self-hosted Rust server that acts as the gas abstraction and settlement layer for all on-chain payment and identity operations on Execution Market.

Role in the System

Agent signs EIP-3009 auth → x402 SDK → Facilitator → On-chain TX (Facilitator pays gas)

The Facilitator:

Receives signed EIP-3009 authorizations from the EM backend
Validates them (amount, nonce, expiry, recipient, chain ID)
Submits the transaction on-chain using its own EOA wallet
Returns the transaction hash

Neither agents nor workers ever pay gas.

URL

https://facilitator.ultravioletadao.xyz

Current version: v1.40.0 · Swagger: https://facilitator.ultravioletadao.xyz/docs/

Facilitator EOA

0x103040545AC5031A11E8C03dd11324C7333a13C7

This wallet pays gas for all Execution Market transactions on all supported networks.

Endpoints

Endpoint	Method	Purpose
`GET /health`	GET	Health check
`GET /version`	GET	Current version
`GET /supported`	GET	List all supported networks and tokens
`POST /verify`	POST	Verify a signed EIP-3009 authorization
`POST /settle`	POST	Submit a settlement (direct, escrow authorize/release/refund)
`POST /accepts`	POST	Negotiate payment requirements (Faremeter middleware)
`POST /escrow/state`	POST	Query on-chain escrow state (read-only)
`POST /register`	POST	Register an ERC-8004 agent identity
`POST /feedback`	POST	Submit ERC-8004 reputation feedback
`GET /feedback`	GET	List ERC-8004 supported networks
`GET /reputation/:network/:agentId`	GET	Query on-chain reputation score
`GET /identity/:network/:agentId`	GET	Query agent identity
`GET /blacklist`	GET	OFAC sanctioned addresses

Network Format

The facilitator accepts two network name formats:

Format	Example	Notes
v1 name	`base`	Human-readable shorthand
CAIP-2	`eip155:8453`	Used in escrow payloads, canonical

Both formats are accepted by all endpoints. CAIP-2 is required in escrow paymentRequirements.network.

Supported Networks

Mainnets (19 EVM + Non-EVM)

Network	Chain ID	CAIP-2	EM Escrow
Base	8453	`eip155:8453`	Yes (PaymentOperator)
Ethereum	1	`eip155:1`	Yes
Polygon	137	`eip155:137`	Yes
Arbitrum	42161	`eip155:42161`	Yes
Avalanche	43114	`eip155:43114`	Yes
Optimism	10	`eip155:10`	Yes
Celo	42220	`eip155:42220`	Yes
Monad	10143	`eip155:10143`	Yes
HyperEVM	999	`eip155:999`	—
Unichain	130	`eip155:130`	—
BSC	56	`eip155:56`	—
SKALE Base	1187947933	`eip155:1187947933`	—
Scroll	534352	`eip155:534352`	—
Solana	—	`solana:mainnet`	Direct SPL only
Sui	—	—	—
Fogo	—	—	—
NEAR	—	—	—
Stellar	—	—	—
Algorand	—	—	—

Execution Market uses 8 EVM mainnets with escrow + Solana (direct SPL transfers, no escrow).

Testnets (17)

Base Sepolia, Ethereum Sepolia, Arbitrum Sepolia, Optimism Sepolia, Polygon Amoy, Avalanche Fuji, Celo Alfajores, HyperEVM Testnet, Unichain Sepolia, SKALE Base Sepolia, Solana Devnet, NEAR Testnet, Stellar Testnet, Algorand Testnet, Sui Testnet, Fogo Testnet, Monad Testnet.

Supported Stablecoins

Token	Networks
USDC	All 19 networks
AUSD	Ethereum, Polygon, Arbitrum, Avalanche, Monad, BSC, Solana, Sui
EURC	Ethereum, Base, Avalanche
USDT	Arbitrum, Celo, Optimism
PYUSD	Ethereum

Full Matrix:

Network	USDC	AUSD	EURC	USDT	PYUSD
Ethereum	Y	Y	Y	—	Y
Base	Y	—	Y	—	—
Arbitrum	Y	Y	—	Y	—
Optimism	Y	—	—	Y	—
Polygon	Y	Y	—	—	—
Avalanche	Y	Y	Y	—	—
Celo	Y	—	—	Y	—
BSC	Y	Y	—	—	—
Monad	Y	Y	—	—	—
HyperEVM	Y	—	—	—	—
Unichain	Y	—	—	—	—
Solana	Y	Y	—	—	—
Sui	Y	Y	—	—	—

Direct Payment (Fase 1)

Standard EIP-3009 settlement — used by Execution Market's default fase1 payment mode.

Agent wallet → (signs EIP-3009) → Facilitator → transferWithAuthorization() → Worker wallet

python

import hashlib

# Generate a unique nonce
nonce = "0x" + hashlib.sha256(f"{task_id}:worker:{timestamp}".encode()).hexdigest()

# POST /settle
{
  "x402Version": 1,
  "scheme": "exact",
  "payload": {
    "authorization": {
      "from": "0xAGENT",
      "to":   "0xWORKER",
      "value": "87000",        # 6-decimal USDC (e.g. $0.087)
      "validAfter": 0,
      "validBefore": deadline,
      "nonce": nonce
    },
    "signature": "0x...",
    "token": "0xUSDC_ADDRESS"
  },
  "paymentRequirements": {
    "scheme": "exact",
    "network": "base",
    "maxAmountRequired": "87000"
  }
}

Nonce rules:

Must be unique per settlement — never reuse, even on failure
Recommended: keccak256(taskId + ":" + type + ":" + timestamp)
If a settlement fails, generate a fresh nonce before retrying

Escrow Lifecycle (Fase 2 / Fase 5)

Used when EM_PAYMENT_MODE=fase2 or fase5. Funds are locked on-chain at task creation and released atomically at approval.

authorize — Lock funds at task creation

json

{
  "x402Version": 2,
  "scheme": "escrow",
  "action": "authorize",
  "payload": {
    "authorization": {
      "from": "0xAGENT_ADDRESS",
      "to": "0xTOKEN_COLLECTOR",
      "value": "1000000",
      "validAfter": "0",
      "validBefore": "1738500000",
      "nonce": "0x..."
    },
    "signature": "0x...",
    "paymentInfo": {
      "operator": "0xOPERATOR_ADDRESS",
      "receiver": "0xWORKER_ADDRESS",
      "token": "0xUSDC_ADDRESS",
      "maxAmount": "1000000",
      "preApprovalExpiry": 281474976710655,
      "authorizationExpiry": 281474976710655,
      "refundExpiry": 281474976710655,
      "minFeeBps": 0,
      "maxFeeBps": 1300,
      "feeReceiver": "0xOPERATOR_ADDRESS",
      "salt": "0x..."
    }
  },
  "paymentRequirements": {
    "scheme": "escrow",
    "network": "eip155:8453",
    "extra": {
      "escrowAddress": "0xESCROW_ADDRESS",
      "operatorAddress": "0xOPERATOR_ADDRESS",
      "tokenCollector": "0xTOKEN_COLLECTOR"
    }
  }
}

release — Send funds to worker on approval

No EIP-3009 signature required — the operator contract authorizes the release.

json

{
  "x402Version": 2,
  "scheme": "escrow",
  "action": "release",
  "payload": {
    "paymentInfo": {
      "operator": "0xOPERATOR_ADDRESS",
      "receiver": "0xWORKER_ADDRESS",
      "token": "0xUSDC_ADDRESS",
      "maxAmount": "1000000",
      "preApprovalExpiry": 281474976710655,
      "authorizationExpiry": 281474976710655,
      "refundExpiry": 281474976710655,
      "minFeeBps": 0,
      "maxFeeBps": 1300,
      "feeReceiver": "0xOPERATOR_ADDRESS",
      "salt": "0x..."
    },
    "payer": "0xAGENT_ADDRESS",
    "amount": "1000000"
  },
  "paymentRequirements": {
    "scheme": "escrow",
    "network": "eip155:8453",
    "extra": {
      "escrowAddress": "0xESCROW_ADDRESS",
      "operatorAddress": "0xOPERATOR_ADDRESS",
      "tokenCollector": "0xTOKEN_COLLECTOR"
    }
  }
}

refundInEscrow — Return funds to agent on cancel

Same structure as release but with "action": "refundInEscrow".

json

{
  "x402Version": 2,
  "scheme": "escrow",
  "action": "refundInEscrow",
  "payload": { "...same as release..." },
  "paymentRequirements": { "...same as release..." }
}

POST /escrow/state — Query on-chain state

Read-only, no gas. Use to verify escrow status before attempting release/refund.

Request:

json

{
  "paymentInfo": { "...paymentInfo object..." },
  "payer": "0xAGENT_ADDRESS",
  "network": "eip155:8453",
  "extra": {
    "escrowAddress": "0xESCROW_ADDRESS",
    "operatorAddress": "0xOPERATOR_ADDRESS",
    "tokenCollector": "0xTOKEN_COLLECTOR"
  }
}

Response:

json

{
  "hasCollectedPayment": false,
  "capturableAmount": "1000000",
  "refundableAmount": "0",
  "paymentInfoHash": "0xabcdef...",
  "network": "eip155:8453"
}

/accepts Endpoint (Faremeter Middleware)

POST /accepts — Added in v1.36.0 for compatibility with @faremeter/middleware.

The endpoint receives merchant payment requirements and returns the subset the facilitator can fulfill, enriched with facilitator data (fee payer, token details, escrow contracts). Both v1 ("base") and CAIP-2 ("eip155:8453") network formats are accepted.

bash

curl -X POST https://facilitator.ultravioletadao.xyz/accepts \
  -H "Content-Type: application/json" \
  -d '{
    "paymentRequirements": [{
      "scheme": "exact",
      "network": "base",
      "maxAmountRequired": "100000",
      "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"
    }]
  }'

ERC-8004 Identity & Reputation

The facilitator provides gasless [[erc-8004|ERC-8004]] operations across 18 networks (16 EVM + Solana mainnet + Solana devnet).

ERC-8004 Supported Networks (16 EVM)

Network	Type	Identity Registry	Reputation Registry
Ethereum	Mainnet	`0x8004A169...9a432`	`0x8004BAa1...dE9b63`
Base	Mainnet	Same (CREATE2)	Same (CREATE2)
Polygon	Mainnet	Same	Same
Arbitrum	Mainnet	Same	Same
Celo	Mainnet	Same	Same
BSC	Mainnet	Same	Same
Monad	Mainnet	Same	Same
Avalanche	Mainnet	Same	Same
Ethereum Sepolia	Testnet	`0x8004A818...4BD9e`	`0x8004B663...8713`
Base Sepolia	Testnet	Same	Same
Polygon Amoy	Testnet	Same	Same
Arbitrum Sepolia	Testnet	Same	Same
Celo Alfajores	Testnet	Same	Same
Avalanche Fuji	Testnet	Same	Same

All mainnet contracts are CREATE2 deterministic — same address on every EVM chain.

Solana ERC-8004 (v1.37.0+)

Solana uses the QuantuLabs 8004-solana Anchor program for identity + reputation:

Agent Registry: 8oo4dC4JvBLwy5tGgiH3WwK4B9PWxL9Z4XjA2jzkQMbQ
ATOM Engine: AToMw53aiPQ8j7iHVb4fGt6nzUNxUhcPc3tbPBZuzVVb

Features: ATOM Engine trust scoring (tiers 0-4: Unknown → Trusted), feedback submission via give_feedback, revoke via POST /feedback/revoke, registration mints a Metaplex Core NFT. Facilitator pays SOL gas.

ERC-8004 Endpoints

bash

# Register agent
POST /register
{ "network": "base", "agentId": "2106", "metadata": { "name": "...", "uri": "..." } }

# Submit feedback (agent → worker or worker → agent)
POST /feedback
{ "network": "base", "agentId": "2106", "rating": 5, "tags": ["quality"], "proofOfPayment": "0x..." }

# Query reputation
GET /reputation/base/2106

# Query identity
GET /identity/base/2106

PaymentOperator Registration

Execution Market's PaymentOperators are registered in the Facilitator's allowlist on all 8 EVM chains:

Network	PaymentOperator
Base	`0x271f9fa7f8907aCf178CCFB470076D9129D8F0Eb`
Ethereum	`0x69B67962ffb7c5C7078ff348a87DF604dfA8001b`
Polygon	`0xB87F1ECC85f074e50df3DD16A1F40e4e1EC4102e`
Arbitrum	`0xC2377a9Db1de2520BD6b2756eD012f4E82F7938e`
Avalanche	`0xC2377a9Db1de2520BD6b2756eD012f4E82F7938e`
Monad	`0x9620Dbe2BB549E1d080Dc8e7982623A9e1Df8cC3`
Celo	`0xC2377a9Db1de2520BD6b2756eD012f4E82F7938e`
Optimism	`0xC2377a9Db1de2520BD6b2756eD012f4E82F7938e`

The StaticFeeCalculator (1300 bps = 13%) is deployed at 0xd643DB63028Cd1852AAFe62A0E3d2A5238d7465A on Base. It splits each release atomically: 87% to worker, 13% to operator (flushed to treasury via distributeFees()).

Security Model

The Facilitator cannot steal funds:

It can only submit exactly what was authorized by the EIP-3009 signature
Each signature is cryptographically bound to: amount, recipient, deadline, nonce, chain ID
Even with the Facilitator EOA key compromised, an attacker cannot move more than what was signed
Escrow: all client-provided addresses are validated against hardcoded contract addresses before any TX is sent

Error Reference

Error	Meaning	Action
`insufficient_balance`	Agent USDC balance too low	Fund the wallet
`invalid_signature`	EIP-3009 sig invalid	Check signing code
`expired_authorization`	Auth deadline passed	Re-sign with new deadline
`nonce_already_used`	Nonce already consumed	Generate a new nonce
`operator_not_registered`	PaymentOperator not allowlisted	Contact Ultravioleta DAO
`FeatureDisabled`	`ENABLE_PAYMENT_OPERATOR=true` not set	Enable operator feature
`UnsupportedNetwork`	No escrow contracts or operator on this chain	Check `/supported`
`UnknownAction`	Invalid action string	Valid: `authorize`, `release`, `refundInEscrow`
`PaymentInfoInvalid`	Address mismatch vs hardcoded deployments	Check operator/escrow addresses
`ContractCall`	On-chain transaction reverted	Check chain state + balances

Chain-Specific Payment Protocols

Chain type	Protocol	Notes
EVM	EIP-3009 `transferWithAuthorization`	Standard for all EVM chains
Solana	SPL Token + Token2022	USDC (SPL), AUSD (Token2022)
NEAR	NEP-366 meta-transactions	Delegate actions
Stellar	Soroban smart contracts	Authorization on Soroban VM
Algorand	Atomic transaction groups	Fee pooling; Facilitator signs tx0

Facilitator ​

Role in the System ​

URL ​

Facilitator EOA ​

Endpoints ​

Network Format ​

Supported Networks ​

Mainnets (19 EVM + Non-EVM) ​

Testnets (17) ​

Supported Stablecoins ​

Direct Payment (Fase 1) ​

Escrow Lifecycle (Fase 2 / Fase 5) ​

authorize — Lock funds at task creation ​

release — Send funds to worker on approval ​

refundInEscrow — Return funds to agent on cancel ​

POST /escrow/state — Query on-chain state ​

/accepts Endpoint (Faremeter Middleware) ​

ERC-8004 Identity & Reputation ​

ERC-8004 Supported Networks (16 EVM) ​

Solana ERC-8004 (v1.37.0+) ​

ERC-8004 Endpoints ​

PaymentOperator Registration ​

Security Model ​

Error Reference ​

Chain-Specific Payment Protocols ​

Facilitator

Role in the System

URL

Facilitator EOA

Endpoints

Network Format

Supported Networks

Mainnets (19 EVM + Non-EVM)

Testnets (17)

Supported Stablecoins

Direct Payment (Fase 1)

Escrow Lifecycle (Fase 2 / Fase 5)

authorize — Lock funds at task creation

release — Send funds to worker on approval

refundInEscrow — Return funds to agent on cancel

POST /escrow/state — Query on-chain state

/accepts Endpoint (Faremeter Middleware)

ERC-8004 Identity & Reputation

ERC-8004 Supported Networks (16 EVM)

Solana ERC-8004 (v1.37.0+)

ERC-8004 Endpoints

PaymentOperator Registration

Security Model

Error Reference

Chain-Specific Payment Protocols