AI payment processing: How agents pay for APIs with MPP

AI agents are already active online. In PwC’s 2025 survey, 79% of surveyed executives said their companies were adopting AI agents. A study of 177,436 MCP tools also found that the share of action tools rose from 27% to 65% of total usage over a 16-month period. Most supported tasks like editing files, but some enabled higher-stakes activities such as financial transactions. As agents take on more work, they need a way to pay for the services they use.

One of the major pain points in AI payment processing is the human-centric nature of these workflows. When an AI agent needs one-time API access, it has to deal with cumbersome onboarding flows, API key generation, and subscriptions tied to a human account.

The Machine Payments Protocol (MPP), co-authored by Stripe and Tempo, gives agents a machine-readable way to pay for API access. Developers can use its shared payment flow to charge for a single request, ongoing usage, or recurring access.

What MPP is

MPP is an open protocol for machine-to-machine payments. When an AI agent requests a paid service, the server returns machine-readable payment instructions that the client can fulfill using a supported payment method.

At the heart of the HTTP flow is the HTTP 402 Payment Required status code. MPP uses this response to tell an agent that a resource requires payment and provide the terms needed to complete it.

How MPP works

MPP supports different payment rails and billing models, including sessions for ongoing usage. The basic HTTP workflow follows five steps.

Step one: Request

The MPP process begins when an AI agent submits an HTTP request for a digital service like an API response or a dataset.

Step two: Challenge

Next, the server responds with a 402 Payment Required status code. This lets the agent know that the data is available if it pays the applicable fee. Along with this response comes a machine-readable payment challenge complete with details on how much access costs and ways to pay.

Step three: Fulfillment

The client checks the payment terms against its configured budget and permissions, then fulfills the challenge using a supported payment method. If the terms exceed those limits or sufficient funds are unavailable, it stops or requests approval.

Step four: Credential

The client creates a payment credential containing the method-specific payment proof or authorization, then retries the original request with that credential in the Authorization header.

Step five: Delivery

The server verifies the credential and payment. If verification succeeds, it returns the requested resource and a payment receipt.

Why MPP matters

Here are a few MPP features that make the entire agent payment process smoother:

• Simplified workflows. MPP brings payment negotiation into the API request-response flow, allowing AI payments to happen within the application.

• Flexible billing. Providers can monetize their APIs with microtransactions, metered sessions, or subscriptions, depending on the payment method. Clients can pay for a single request or authorize ongoing access.

• Familiar integration points. Developers can add payment verification to existing API routes using MPP middleware. The application still controls access, request validation, and how the service is delivered.

The payment rails underneath MPP

MPP is payment-method agnostic: the same challenge-and-credential flow can work with different payment rails. It is also transport agnostic, with bindings for HTTP, MCP, and WebSockets. The payment method determines how money moves; the transport determines how the client and server exchange messages.

Supported payment methods include card payments through Stripe and digital assets like stablecoins on Tempo. Developers can choose the method that fits their customers and billing model.

Fiat and card rails

Stripe’s MPP integration supports card payments using Shared Payment Tokens. These tokens let an agent initiate a payment without exposing the underlying card details.

Shared Payment Tokens grant scoped access to a payment method, with usage and expiration limits. The server uses the token to process the payment through Stripe, where it appears alongside the business’s other payments.

Blockchain rails

For frequent API calls, blockchain payment rails can support small payments with near-instant onchain settlement. Tempo is a layer-1 blockchain built for payments, with sub-cent fees for standard stablecoin transfers and network fees paid in supported stablecoins.

For high-frequency usage, MPP sessions on Tempo let clients authorize multiple payments through a funded channel. Signed offchain vouchers track cumulative spending, and the provider can settle the aggregate onchain. This reduces the need for a separate onchain transaction for every API call.

Building agent-ready APIs with MPP

Developers can add MPP payment verification to existing APIs through middleware or a gateway. The payment flow works alongside the application’s authentication, authorization, and billing logic.

Depending on your application, there are three ways of implementing MPP:

• API gateway pattern. The most straightforward integration is to put MPP in front of your existing API using an API gateway. With this strategy, your gateway manages the payment workflow while your application focuses on serving requests.

• Per-endpoint pattern. For more fine-grained control over how to monetize your API, you could choose which routes require payment while keeping others free. For instance, if you have premium models or compute-intensive operations, you could trigger an MPP payment flow for these specific use cases.

• MCP tool monetization. Since many agents already interact with services via the Model Context Protocol (MCP), using an MCP server linked to MPP transforms APIs into on-demand products. When agents invoke a paid tool, the MCP server responds with an MPP payment challenge, creating a new pay-per-use monetization strategy at the protocol level.

Choosing between one-time payments, sessions, and subscriptions

A one-time payment fits a single API response, report, or compute job. The server quotes a price, the client fulfills the payment challenge, and the server delivers the resource after verification.

Sessions suit repeated requests and metered usage, such as streamed model output. On Tempo, the client funds a payment channel and signs cumulative offchain vouchers as usage grows. The provider can settle those vouchers onchain, making sessions useful for high-frequency micropayments.

Subscriptions on Tempo provide recurring access at a fixed price. The client authorizes recurring payment terms once, and the server can collect at most one charge per billing period. This supports API plans, memberships, and access bundles without a separate payment for every request.

MPP for AI agents: Making every API call count

Human interactions are holding back the agentic economy. While it’s simple enough to create an account or manage API keys, AI agents can’t operate at scale if payment solutions aren’t machine-readable and programmable. MPP is paving the way for developers to bring automation into AI payments through a standard HTTP workflow.

The payment protocol works alongside the infrastructure that moves funds. Tempo supports stablecoin payments with near-instant onchain settlement, sub-cent fees for standard transfers, and dedicated payment lanes. With MPP sessions, providers can also meter frequent API calls and settle aggregate usage onchain.

See how Tempo can take your agentic payment strategy from concept to reality.

FAQ

What’s AI payment processing?

In this context, AI payment processing means an agent initiates and completes payments for services within permissions and spending limits set by a person or business.

Do agents need cryptocurrency to use MPP?

No. MPP supports payment methods such as card payments through Stripe, as well as blockchain payments. The available options depend on the methods implemented by the client and server.

What blockchains support MPP for AI agent transactions?

MPP supports stablecoin payments on Tempo and has documented payment methods for other networks, including Solana and the Bitcoin Lightning Network. Supported assets and billing models vary by payment method.

How do AI agents authenticate and pay for API calls autonomously?

The client fulfills the server’s payment challenge and sends a method-specific credential with its request. The server verifies the payment before delivering the resource. Application authentication and spending permissions remain part of the surrounding integration.

Is MPP a replacement for traditional payment systems?

MPP complements the current payment infrastructure by providing a machine-native way for AI agents to pay for services, but it isn’t a replacement for traditional payment systems.