--- title: "Stripe MPP: How Agents Pay for a Fax | SingleFax" description: "Compare Stripe MPP agent payments with hosted checkout. See how SingleFax handles HTTP 402 challenges, payment credentials and fax submission." canonical_url: "https://singlefax.com/blog/stripe-machine-payments-protocol" last_updated: 2026-09-04 locale: en meta: "og:description": "Compare Stripe MPP agent payments with hosted checkout. See how SingleFax handles HTTP 402 challenges, payment credentials and fax submission." "og:image": "https://singlefax.com/images/versioned/c69b3699ffe82eda/stripe-machine-payments-protocol.jpg" "og:image:alt": "Stripe MPP: How Agents Pay for a Fax" "og:image:height": "800" "og:image:type": image/jpeg "og:image:width": "1200" "og:title": "Stripe MPP: How Agents Pay for a Fax" --- > Index of every page on this site: [llms.txt](https://singlefax.com/llms.txt) [singlefax](https://singlefax.com/) [Send & receive](https://singlefax.com/send-or-receive-fax) [For companies](https://singlefax.com/for-companies)Solutions [Pricing](https://singlefax.com/pricing) [Blog](https://singlefax.com/blog) [Sign in](https://singlefax.com/login) [All guides](https://singlefax.com/blog) # Stripe MPP vs Instant Checkout: How Agents Pay for a Fax UpdatedSep 4, 2026 [![Mircea Rilă](https://singlefax.com/images/authors/mircea-rila.jpg)Mircea Rilă](https://singlefax.com/authors/mircea-rila) Compare Stripe MPP agent payments with hosted checkout. See how SingleFax handles HTTP 402 challenges, payment credentials and fax submission. ![Stripe MPP vs Instant Checkout: How Agents Pay for a Fax](https://singlefax.com/images/versioned/c69b3699ffe82eda/stripe-machine-payments-protocol.jpg) **Stripe Link CLI** is the main card path that can pay MPP-enabled services with Stripe today. Tempo Wallet, Privy, AgentCash, and Kite Passport pay the Tempo / USDC.e challenge on the same URL. **MPP** (Machine Payments Protocol) is the HTTP 402 flow Stripe co-authored with Tempo. The Stripe rail uses **Shared Payment Tokens (SPTs)**, scoped card credentials from a Link wallet, not a normal checkout page. **ChatGPT Instant Checkout** is a different Stripe product (ACP). It is shopping in a chat UI, not the 402 API protocol. SingleFax supports the human-facing patterns that matter here: MCP + Checkout for chat apps, API keys + credits for backends, and MPP on `POST /api/v1/machine/faxes` for agents that can mint an SPT **or** pay Tempo USDC. Do **not** send PHI on MCP, MPP, or the public API. Covered Entities use [HIPAA Secure Mode](https://singlefax.com/hipaa-fax) on the website with an electronic BAA. ## Three ways to pay at SingleFax | You are… | Pay with | Entry | | --- | --- | --- | | In Cursor, Claude, Codex, ChatGPT, or VS Code | Hosted Checkout, or leftover subscription pages | MCP at `/mcp`, [install](https://singlefax.com/agents) | | Writing a script or backend | Prepaid credits | API key, [developers](https://singlefax.com/developers) | | An agent that can mint a Stripe SPT or pay Tempo USDC | HTTP 402 → retry | `POST /api/v1/machine/faxes`, [mpp.md](https://singlefax.com/mpp.md) | MPP does not replace MCP. Chat MCP tools return JSON. Link CLI needs a URL that returns **HTTP 402** and `WWW-Authenticate`. Point `mpp pay` at the machine fax route, never at `/mcp`. ## What MPP is An agent requests a paid resource with no credential. The server answers **402 Payment Required** with the amount, currency, and Stripe network / profile. The agent (usually Link CLI) mints an SPT from the user’s Link wallet. A human approves that spend in the **Link app**. The client retries with `Authorization: Payment …`. The merchant creates a Stripe PaymentIntent. Funds land in the merchant’s normal Stripe balance. That is the Stripe card rail. The same 402 also offers Tempo / USDC.e. Tempo Wallet, Privy, AgentCash, and Kite Passport pay that challenge. Stripe offramps into the merchant’s normal Stripe balance. Official references: [Stripe MPP](https://docs.stripe.com/payments/machine/mpp), [Link CLI machine payments](https://docs.stripe.com/agentic-commerce/link-cli/machine-payments), [Shared Payment Tokens](https://docs.stripe.com/agentic-commerce/concepts/shared-payment-tokens), [mpp.dev](https://mpp.dev). ## How the Stripe path works 1. Service returns HTTP 402 with a Stripe challenge (amount, currency, network / profile ID). 2. Link CLI (or an agent wrapping it) creates an SPT from the user’s Link wallet. 3. User approves in the Link app. 4. Client retries with the credential. The merchant creates a PaymentIntent. The fax is queued. At SingleFax the URL is: ``` POST https://singlefax.com/api/v1/machine/faxes ``` Body is JSON `{ "to": "", "base64": "", "request_id": "" }`. Use a real destination (not `+1555…`) and the original file (Word, Excel, PDF, image, or text, do not convert to PDF first). Reusing a `request_id` with a different body returns 409. Stripe SPT has a $0.50 minimum; SingleFax’s retail floor is $0.99. Install and pay: ``` npx skills add stripe/link-cli # or: npx @stripe/link-cli --mcp npx @stripe/link-cli auth login npx @stripe/link-cli mpp pay https://singlefax.com/api/v1/machine/faxes \ -X POST \ -d '{"to":"+14155552671","base64":"","request_id":"mpp-1"}' \ --context "Send a fax via SingleFax after the user asked this agent to pay for the send." ``` US Link account required. Commands and challenge shapes: [agents § MPP](https://singlefax.com/agents#mpp) and [mpp.md](https://singlefax.com/mpp.md). ## What actually supports Stripe MPP | Tool | Stripe MPP | Notes | | --- | --- | --- | | **Link CLI** (`link-cli mpp pay`) | Yes, native `stripe.charge` / SPT | Parses the 402, creates an SPT, retries. User approves each spend in the Link app. Can run as an MCP server. US Link accounts. | | **Tempo Wallet / Privy / AgentCash / Kite Passport** | Tempo `tempo/charge` | Pay the Tempo challenge on the same machine URL. USDC.e on Tempo mainnet. | | **mppx CLI** | Yes | Dev / debug client; Stripe charge and Tempo. | | **Claude Code** | Yes, via Link CLI MCP + Stripe plugin | Official card integration path. Tempo CLI also works. | | **Cursor / Codex** | Yes, via Stripe plugin + Link CLI | Same pattern: agent drives Link, human approves. Cursor cannot mint an SPT alone. Tempo wallets still pay the Tempo challenge. | | **ChatGPT custom MCP** | No (use Checkout) | Developer-mode connectors call SingleFax MCP. Payment is a Checkout URL, not Instant Checkout and not MPP. | | **Grok Bot / shopping Link** | Link for purchases | Uses Link for single-use cards / tokens with human approval. Shopping-oriented; MPP SPT is the same Link stack, not ChatGPT Instant Checkout. | ## MPP vs ACP (Instant Checkout) | | **MPP** | **ACP / Instant Checkout** | | --- | --- | --- | | What it is | HTTP 402 on an API | Stripe Agentic Commerce Protocol for in-chat shopping | | Where it runs | Any client that can retry a 402 | ChatGPT Instant Checkout and similar shop UIs | | Credential | Shared Payment Token from Link (or Tempo on other rails) | Also uses SPTs, for a checkout session, not a 402 API | | Human in the loop | Link app for SPT; wallet signature for Tempo | Confirms in the chat checkout UI | | SingleFax | Live on `POST /api/v1/machine/faxes` | Not used. ChatGPT MCP still returns a SingleFax Checkout URL | If someone says “the agent paid with Stripe in ChatGPT,” they usually mean Instant Checkout or a hosted Checkout link, not MPP. ## When to use which **Use MCP** when a person is in Cursor, Claude, Codex, ChatGPT, or VS Code and you want the assistant to upload the original document (Word, Excel, PDF, or an image, do not convert to PDF first) and either open Checkout or spend leftover subscription pages. That is the default. [Install MCP](https://singlefax.com/agents). **Use MPP** when the agent can run Link CLI or a Tempo wallet and you want pay-per-fax without creating a SingleFax API key. Typical: Claude Code or Cursor with a terminal and a US Link account, or a Tempo Wallet / Privy / AgentCash / Kite Passport client. **Use the REST API + CLI** when the sender is *your* service: workers, cron, an internal tool. Create a key, prepay credits, no 402. [Developer docs](https://singlefax.com/developers). **Do not use MPP** for PHI, for ChatGPT Instant Checkout, or by pointing Link CLI at `/mcp`. ## Use cases with SingleFax **1. “Fax this document” in Claude Code or Cursor** Add SingleFax MCP for quote + draft. If you want the *agent* to pay instead of opening Checkout, add Link CLI and `mpp pay` the machine URL. You still approve in Link. Same $0.99 retail floor as the website. **2. A backend that should not hold a card** Prefer [API keys and credits](https://singlefax.com/developers). MPP is for agents with a Link wallet or a Tempo USDC wallet, not for storing customer cards on your server. **3. A one-off government or court fax from an agent** IRS and many courts still take fax. The agent can assemble the PDF and pay per send. Confirm the destination on the agency site. This path is **not** HIPAA; do not put medical records on MPP. **4. ChatGPT Developer Mode** Custom MCP works for tools. Payment is Checkout. Instant Checkout is a merchant shopping integration SingleFax does not use. ## Related - [Install MCP (Cursor, Claude, Codex, ChatGPT, VS Code)](https://singlefax.com/agents) - [MPP command reference (mpp.md)](https://singlefax.com/mpp.md) - [REST API, CLI, and language examples](https://singlefax.com/developers) - [Send a fax with AI agents and MCP](https://singlefax.com/blog/send-fax-with-ai-agents-mcp) - [Pay-per-fax vs subscription](https://singlefax.com/blog/pay-per-fax-vs-subscription) ## Frequently asked questions Can an AI agent pay SingleFax with Stripe MPP today? Yes. Point Stripe Link CLI or a Tempo wallet at POST /api/v1/machine/faxes. The server returns HTTP 402 with Stripe SPT and Tempo challenges. Link creates a Shared Payment Token (approve in the Link app); Tempo wallets pay USDC.e. The fax queues. Chat apps should use MCP plus Checkout instead. Do not send PHI on MPP. Is Stripe MPP the same as ChatGPT Instant Checkout? No. Instant Checkout uses Stripe’s Agentic Commerce Protocol (ACP) for in-chat shopping. MPP is an HTTP 402 challenge on an API. SingleFax machine faxes use MPP, not Instant Checkout. Can Cursor pay MPP by itself? Cursor cannot mint a Stripe Shared Payment Token on its own. Install Stripe Link CLI and approve in the Link app, or pay the Tempo USDC.e challenge from Tempo Wallet, Privy, AgentCash, or Kite Passport. Chat apps should still default to MCP plus Checkout. Can agents pay SingleFax with crypto or Tempo? Yes, on the machine fax path. POST /api/v1/machine/faxes returns HTTP 402 with a Tempo USDC.e challenge alongside Stripe SPT. Tempo Wallet, Privy, AgentCash, and Kite Passport can pay. Website Checkout for humans is still card, Apple Pay, Google Pay, or Link, not Bitcoin or other chains. When should I use MCP instead of MPP? Use MCP for Cursor, Claude, Codex, ChatGPT, and VS Code. The agent returns a Checkout link, or sends on your subscription page pool. Use MPP when the client can mint a Shared Payment Token or pay Tempo USDC. Use an API key and prepaid credits for your own backend. ## Sources - [Stripe Machine Payments Protocol](https://docs.stripe.com/payments/machine/mpp) - [Pay machine-payment merchants with Link CLI](https://docs.stripe.com/agentic-commerce/link-cli/machine-payments) - [Shared Payment Tokens](https://docs.stripe.com/agentic-commerce/concepts/shared-payment-tokens) - [Link for agents](https://link.com/agents) - [MPP specification](https://mpp.dev) - [Tempo CLI](https://tempo.xyz/developers/docs/cli) ## Send a fax [Send a fax](https://singlefax.com/send-or-receive-fax?type=send) [Get a US or Canadian number](https://singlefax.com/send-or-receive-fax?type=receive) ## Related guides [

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The best free online fax services in 2026 compared: free sending quotas, free receiving numbers, page caps, expiry and catches, in one table.Oct 15, 2026](https://singlefax.com/blog/best-free-online-fax-services) [singlefax](https://singlefax.com/) Send once. Receive when you need to. [![Get it on Google Play](https://singlefax.com/images/google-play-badge.png)](https://play.google.com/store/apps/details?id=com.monocube.singlefax) [Add to Chrome](https://chromewebstore.google.com/detail/singlefax-fax-a-document/ojpmpilgkmjcfebhpkdmmjlkbcifkkej) [SingleFax on LinkedIn](https://www.linkedin.com/company/singlefax/) [SingleFax on Facebook](https://www.facebook.com/singlefax) [SingleFax on Instagram](https://www.instagram.com/singlefax.app) [SingleFax on Threads](https://www.threads.com/@singlefax.app) [SingleFax on YouTube](https://www.youtube.com/@singlefax) [SingleFax on GitHub](https://github.com/SingleFax) ## Fax services - [Send a fax](https://singlefax.com/send-or-receive-fax?type=send) - [Receive faxes](https://singlefax.com/send-or-receive-fax?type=receive) - [Free 24-hour number](https://singlefax.com/free-fax-number) - [Lifetime number](https://singlefax.com/lifetime-fax-number) - [Number porting](https://singlefax.com/number-porting) - [Test fax](https://singlefax.com/test-fax-number) - [Company plans](https://singlefax.com/for-companies) - [HIPAA Secure](https://singlefax.com/hipaa-fax) - [Online fax](https://singlefax.com/online-fax) - [Email to fax](https://singlefax.com/email-to-fax) - [WhatsApp to fax](https://singlefax.com/whatsapp-to-fax) ## IRS filings - [All IRS filings](https://singlefax.com/irs-filings) - [EIN · Form SS-4](https://singlefax.com/get-ein) - [Form 5472](https://singlefax.com/file-5472) - [Form 7004](https://singlefax.com/file-7004) - [Form 2553](https://singlefax.com/file-2553) - [Form 2848](https://singlefax.com/file-2848) - [Form 4506-T](https://singlefax.com/file-4506-t) - [Form 8821](https://singlefax.com/file-8821) - [Form 8802](https://singlefax.com/file-8802) - [Form 8655](https://singlefax.com/file-8655) - [Form 3911](https://singlefax.com/file-3911) - [Form 8233](https://singlefax.com/file-8233) - [NY POA-1](https://singlefax.com/file-ny-poa-1) ## Tools & resources - [Free fax tools](https://singlefax.com/free-fax-tools) - [Prepare a fax PDF](https://singlefax.com/prepare-fax) - [Printable test page](https://singlefax.com/fax-test-page) - [Cover sheets](https://singlefax.com/fax-cover-sheet) - [Mobile app](https://singlefax.com/mobile-app) - [Chrome extension](https://singlefax.com/chrome-extension) - [Developers](https://singlefax.com/developers) - [AI fax agents](https://singlefax.com/agents) - [Versioning](https://singlefax.com/versioning) - [Congress fax directory](https://singlefax.com/fax/congress) - [Senate fax directory](https://singlefax.com/fax/senate) - [Governor fax directory](https://singlefax.com/fax/governors) ## SingleFax - [Pricing](https://singlefax.com/pricing) - [Blog](https://singlefax.com/blog) - [About](https://singlefax.com/about) - [Contact](https://singlefax.com/contact) - [Support](https://singlefax.com/support) © 2026 SingleFax [Privacy](https://singlefax.com/privacy-policy) [Terms](https://singlefax.com/terms-of-service) [Refunds](https://singlefax.com/refund-policy) [Report abuse](https://singlefax.com/abuse) ```json {"@context":"https://schema.org","@graph":[{"@id":"https://singlefax.com/#website","@type":"WebSite","description":"SingleFax lets you send and receive one time faxes from your phone or computer. 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