> ## Documentation Index > Fetch the complete documentation index at: https://aomi.dev/docs/llms.txt > Use this file to discover all available pages before exploring further. # x402 and MPP > Learn how Aomi batches App tool fees and settles them through x402 or MPP. Aomi turns successful priced tool calls into a running balance. It can settle that balance through x402 or MPP. The accounting is the same in both flows; the difference is when the payment gate runs relative to the API call. Your App declares a tool price and beneficiary in `.pricing.toml`. The price determines how many credits a successful call adds to the balance. The beneficiary identifies the wallet that receives the payment. Blocked and failed calls remain free. ## x402 and MPP use the same balance x402 is a pre-check gate. At a settlement checkpoint, Aomi verifies the balance before serving the request. If payment is required, the request stops with `402 Payment Required` until the user authorizes payment and retries it. MPP is a post-check settlement flow. The API call runs first, then Aomi reconciles the resulting balance on the trailing edge. Both variants preserve the same App, tool, user, and beneficiary attribution. x402 checks before an API call while MPP settles after the call ## Why Aomi uses settlement checkpoints A strict x402 integration checks and settles every request. That gives zero credit exposure, but it also adds a payment round trip to every turn. Aomi can defer the gate to a settlement checkpoint and serve the turns between checkpoints immediately. The diagrams call the maximum number of turns between checkpoints `TURN_CAP`. With a cap of three, one turn performs the gate check and the next two use the fast path. Over six turns, this reduces six checks and settlements to two. Comparison of per-request x402 checks with deferred checks every three turns The tradeoff is bounded credit exposure. A balance may become negative after an admitted turn and remain negative until the next checkpoint. A smaller cap reduces that exposure. A cap of one recovers strict per-request x402 behavior. ## The gate logic, per turn For x402, Aomi uses this order: 1. A turn arrives and Aomi determines its cost. 2. If the turn is not a checkpoint, Aomi serves it and records the cost. 3. At a checkpoint, Aomi checks the balance entering the turn. 4. If that balance is zero or positive, Aomi serves the turn, records its cost, and resets the checkpoint counter. 5. If that balance is negative, Aomi returns `402 Payment Required` without serving the turn. The user can top up and retry the same request. Per-turn flow showing the fast path and settlement checkpoint branches In the diagram, the initial deduction represents the turn's provisional usage entry. The x402 admission decision uses the balance at the gate, before that new usage becomes settled debt. This is why a user entering a checkpoint at zero can complete the admitted turn and settle the resulting balance later. ## Running balance across turns Suppose a user begins with one credit and each turn costs five credits. At the first checkpoint, the gate sees `+1`, so the turn is admitted and the balance becomes `-4`. The next two turns use the fast path, moving the balance to `-9` and then `-14`. At turn four, the next checkpoint sees `-14`. x402 blocks the turn with a `402` response. The balance does not fall again because the blocked turn did not run. After the user tops up, the retried request can pass the gate. Running balance across four turns with a deferred x402 checkpoint ## The x402 payment flow When an x402 checkpoint blocks a request, Aomi returns payment requirements to the client. The user authorizes an exact USDC amount, and the client retries the original request with the signed authorization. ```mermaid theme={null} sequenceDiagram autonumber actor User participant Client as Portal or custom client participant Aomi participant Wallet participant Facilitator as x402 facilitator participant Chain as Blockchain participant Beneficiary as App beneficiary User->>Client: Send request Client->>Aomi: Submit request at checkpoint Aomi-->>Client: 402 with Payment-Required Client->>Wallet: Show amount and recipient User->>Wallet: Authorize USDC payment Wallet-->>Client: Payment-Signature Client->>Aomi: Retry the same request with signature Aomi->>Facilitator: Verify and settle authorization Facilitator->>Chain: Submit authorized USDC transfer Chain->>Beneficiary: Credit USDC Chain-->>Facilitator: Return transaction hash Facilitator-->>Aomi: Return settlement receipt Aomi-->>Client: Continue request with Payment-Response ``` The wallet authorization binds the payment to an exact amount, recipient, network, and USDC contract. A change to any signed term invalidates the authorization and prevents the transfer. ## x402 HTTP exchange | Step | HTTP field | Purpose | | ------------ | ---------------------- | ------------------------------------------------------------ | | Challenge | `402 Payment Required` | Stops the checkpoint request until payment is authorized | | Requirements | `Payment-Required` | Describes the accepted network, asset, amount, and recipient | | Signed retry | `Payment-Signature` | Carries the user's wallet authorization | | Receipt | `Payment-Response` | Confirms settlement and identifies the onchain transaction | The facilitator verifies that the signed terms match the original challenge. It then submits the authorized USDC transfer and pays the network gas. The user signs the authorization in their wallet but does not need to submit a separate transaction. ## Who receives the payment The beneficiary in `.pricing.toml` receives the payment directly from the user's wallet. Aomi verifies the payment and records the receipt, but it does not route the funds through an Aomi-owned wallet. The beneficiary controls the revenue as soon as the transfer settles. The wallet displays the network, asset, recipient, and exact amount before the user signs. After settlement, Aomi keeps the App and tool attribution so the builder can match the receipt to its source in Usage. ## Payments across Apps Aomi attributes every fee to the App and tool that produced it. This attribution remains attached to the Usage record even when payment occurs later. For settlement, Aomi groups outstanding fees by user and beneficiary wallet. If several Apps use the same beneficiary, one settlement can cover fees from more than one App. Each fee still appears under its original App in Usage. Apps with different beneficiaries remain in separate balances and settle through separate payment requests. ## Tool fees and outcome fees x402 and MPP settle flat tool fees declared under `[resources.]`. A successful tool call adds the configured credit amount to the user's balance for that beneficiary. Aomi converts the balance into the payment amount when it creates a settlement request. Outcome fees follow a different path. Aomi adds an outcome fee to the user's signed smart-account transaction. The fee settles in the asset being moved at the same time as the onchain action, so it does not enter this running balance or require a separate USDC authorization. ## Handle an x402 challenge Aomi's portal handles the full challenge flow for the user. It presents the payment terms, opens the connected wallet, and retries the original request after authorization. It also reads `Payment-Response` and associates the receipt with the completed request. A custom client must treat `402 Payment Required` as an actionable payment state instead of a generic server error. Preserve the original request and retry it with `Payment-Signature` only after the user approves the displayed terms. If verification or settlement fails, keep the request blocked and show the facilitator's error. ## Next Review tool revenue, outcome fees, model costs, and hosting. Add prices and beneficiaries to your App.
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