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Pactum records every billable call your API serves against an end user's prepaid USDC balance held in a smart contract (PactumBilling) on Arc. If the balance can't cover the call, metering refuses with 402 before you spend model tokens. Pending usage settles to your payout wallet in on-chain batches, and every settled row carries its transaction hash  a receipt your customer can verify without trusting you.

Sign up at pactum.rizzgm.xyz → Settings → set your payout wallet → generate an API key 



curl -X POST https://pactum.rizzgm.xyz/api/v1/usage/track \

  -H "X-API-Key: pactum_..." -H "Content-Type: application/json" \

    "completion_price_per_token": 0.000015,

   Expected responses: 200 { "recorded": true, "cost": 0.0112 } · 

replay with the same idempotency_key → "deduplicated": true (never double-charged) · 402 when the user's channel balance can't cover it · 429 when a daily/monthly spend policy caps the charge.

 page as it lands, endpoint, quantity, unit price, cost, and pending → settled status.

Users fund their balance (and withdraw unused funds) at the wallet page: approve USDC → deposit() → userBalances is the channel balance. Full walkthrough

 POST /api/v1/usage/track with an X-API-Key header; token counts and per-token prices are yours, cost is computed in exact 6-decimal integer math.

 same idempotency_key on retries/queue redeliveries returns the original event, not a second charge.

read userBalances(address) directly from the contract (plain viem/ethers call) or GET /api/v1/wallet/balance (API-key or wallet-signature auth) to refuse work before burning tokens.

settlement batches call batchSettleUsage on PactumBilling; each settled event stores its settled_tx_hash with an explorer link.

plain REST from Node/Python/Go; contract calls via viem/ethers; example Express integration in the docs.

GET /api/health reports database + chain (contract VERSION()) status, so you can monitor the deployment you build against.




deployed on Arc Testnet (chain 5042002); no mainnet value at stake.

the settlement operator is a trusted role; the v2 contract mitigates with pausable settlement, a two-step operator hand-off, an on-chain fee cap (default 0 bps), and user withdrawals that 

if the contract isn't configured server-side, metering returns 503 instead of recording unbilled usage.

validation rejects negative/fractional tokens and oversized payloads; costs are computed in integer units, never floats.

solo project, no third-party audit yet; contract is short (~300 lines, self-contained) and open source.

Live demo — Aura AI, chat billed per token: 

0x4bab39e99d9bca6897d8b844f84fbe6b06d28509

Pactum on Arc: per-token billing for AI APIs, settled in USDC

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