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# Transports \[HTTP, MCP, and WebSocket bindings for payment flows]

MPP defines how the Payment authentication scheme operates over different transport protocols. The core protocol targets HTTP, with extensions for other transports like MCP and JSON-RPC.

## Available transports

| Transport | Use Case | Spec |
|-----------|----------|------|
| [HTTP](/protocol/transports/http) | REST APIs, web resources | [RFC 9110](https://www.rfc-editor.org/rfc/rfc9110#section-11) |
| [MCP](/protocol/transports/mcp) | AI tool calls using Model Context Protocol | [MCP Transport Spec](https://paymentauth.org) |
| [WebSocket](/protocol/transports/websocket) | Bidirectional payment streams | [RFC 6455](https://www.rfc-editor.org/rfc/rfc6455) |
| JSON-RPC | Non-MCP JSON-RPC services | [JSON-RPC 2.0](https://www.jsonrpc.org/specification) |

## Transport-agnostic design

MPP's core concepts—Challenges, Credentials, and Receipts—remain the same across transports. The encoding and delivery mechanism changes:

* **HTTP** uses standard headers (`WWW-Authenticate`, `Authorization`, `Payment-Receipt`)
* **MCP** uses JSON-RPC error codes and `_meta` fields
* **WebSocket** uses JSON message framing with an `mpp` discriminator

Choose the transport that matches your protocol. HTTP for REST APIs, MCP for AI agent tool calls, WebSocket for bidirectional payment streams, or JSON-RPC for non-MCP JSON-RPC services.