> ## Documentation Index
> Fetch the complete documentation index at: https://docs.getbindu.com/llms.txt
> Use this file to discover all available pages before exploring further.

# 1.12 Echo Agent Behind Paywall

> Minimal echo agent gated by an x402 paywall on Base Sepolia

The simplest possible x402-paywalled agent. Same echo handler as the basic echo agent, but the `message/send` method is gated: the server returns HTTP 402 with payment requirements until the caller pays the configured amount (`$0.0001` USDC in the example below) on Base Sepolia.

## Code

Create `echo_agent_behind_paywall.py` with the code below, or save it directly from your editor.

```python theme={null}
"""Echo Testing Agent

A minimal Bindu agent for testing connectivity.
Echoes back user input to verify the system is working.

Features:
- Simple echo functionality
- No external dependencies
- Perfect for testing Bindu installation
- Lightweight and fast

Usage:
    python echo_simple_agent.py

Environment:
    No environment variables required
"""

from bindu.penguin.bindufy import bindufy


def handler(messages):
    """Handle incoming messages by echoing back the user's latest input.

    Args:
        messages: List of message dictionaries containing conversation history.

    Returns:
        List containing a single assistant message with the user's content.
    """
    # Reply with the user's latest input
    return [{"role": "assistant", "content": messages[-1]["content"]}]


config = {
    "author": "gaurikasethi88@gmail.com",
    "name": "echo_agent",
    "description": "A basic echo agent for quick testing.",
    "deployment": {
        "url": "http://localhost:3773",
        "expose": True,
        "cors_origins": ["http://localhost:5173"]
    },
    "skills": ["skills/question-answering", "skills/pdf-processing"],
    "execution_cost": {
    "amount": "$0.0001",
    "token": "USDC",
    "network": "base-sepolia",
    "pay_to_address": "0x2654bb8B272f117c514aAc3d4032B1795366BA5d",
    "protected_methods": [
      "message/send"
    ]
  },
}

bindufy(config, handler)

# if you want to use tunnel to expose your agent to the internet, use the following command
#bindufy(config, handler, launch=True)
```

## How It Works

**Handler**

* Same echo logic as the basic echo agent — returns the user's latest message back
* No model call, no external dependencies

**x402 paywall block**

* `execution_cost` in the config declares the price and chain
* `amount`: `$0.0001` charged per request
* `token`: `USDC`
* `network`: `base-sepolia` (testnet — use the Circle faucet for test USDC)
* `pay_to_address`: receiving wallet for the payment
* `protected_methods`: list of A2A methods that require payment; here only `message/send`

**The 402 response cycle**

* Caller sends `message/send` with no payment header
* Server returns **HTTP 402 Payment Required** with x402 `paymentRequirements` describing the price, network, token, and `payTo` address
* Caller signs an x402 payment (EIP-3009 transfer authorization on Base Sepolia) and resends the request with the `X-PAYMENT` header
* Server verifies the signed payment, executes the handler, and returns the JSON-RPC result

**Testing it**

* Fund a Base Sepolia wallet with test USDC from the [Circle USDC faucet](https://faucet.circle.com/)
* Use an x402-aware client to handle the 402 → sign → retry loop automatically
* `tasks/get` is not in `protected_methods`, so it remains free

## Dependencies

```bash theme={null}
uv init
uv add bindu
```

## Environment Setup

No environment variables required for the server. The caller needs a funded Base Sepolia wallet with test USDC.

## Run

```bash theme={null}
uv run echo_agent_behind_paywall.py
```

## Example API Calls

<AccordionGroup>
  <Accordion title="Message Send Request (no payment)">
    ```json theme={null}
    {
      "jsonrpc": "2.0",
      "method": "message/send",
      "params": {
        "message": {
          "role": "user",
          "kind": "message",
          "messageId": "9f11c870-5616-49ad-b187-d93cbb100001",
          "contextId": "9f11c870-5616-49ad-b187-d93cbb100002",
          "taskId": "9f11c870-5616-49ad-b187-d93cbb100003",
          "parts": [
            {
              "kind": "text",
              "text": "Repeat after me: hello paywall"
            }
          ]
        },
        "configuration": {
          "acceptedOutputModes": ["application/json"]
        }
      },
      "id": "9f11c870-5616-49ad-b187-d93cbb100003"
    }
    ```
  </Accordion>

  <Accordion title="402 Payment Required Response">
    ```json theme={null}
    {
      "x402Version": 1,
      "error": "X-PAYMENT header is required",
      "accepts": [
        {
          "scheme": "exact",
          "network": "base-sepolia",
          "maxAmountRequired": "100",
          "resource": "http://localhost:3773/",
          "description": "Payment required for message/send",
          "mimeType": "application/json",
          "payTo": "0x2654bb8B272f117c514aAc3d4032B1795366BA5d",
          "maxTimeoutSeconds": 60,
          "asset": "0x036CbD53842c5426634e7929541eC2318f3dCF7e",
          "extra": {
            "name": "USDC",
            "version": "2"
          }
        }
      ]
    }
    ```
  </Accordion>

  <Accordion title="Message Send Request (with X-PAYMENT header)">
    ```http theme={null}
    POST / HTTP/1.1
    Host: localhost:3773
    Content-Type: application/json
    X-PAYMENT: <base64-encoded-x402-payment-payload>

    {
      "jsonrpc": "2.0",
      "method": "message/send",
      "params": {
        "message": {
          "role": "user",
          "kind": "message",
          "messageId": "9f11c870-5616-49ad-b187-d93cbb100001",
          "contextId": "9f11c870-5616-49ad-b187-d93cbb100002",
          "taskId": "9f11c870-5616-49ad-b187-d93cbb100003",
          "parts": [
            {
              "kind": "text",
              "text": "Repeat after me: hello paywall"
            }
          ]
        },
        "configuration": {
          "acceptedOutputModes": ["application/json"]
        }
      },
      "id": "9f11c870-5616-49ad-b187-d93cbb100003"
    }
    ```
  </Accordion>

  <Accordion title="Successful Response (after payment)">
    ```json theme={null}
    {
      "jsonrpc": "2.0",
      "id": "9f11c870-5616-49ad-b187-d93cbb100003",
      "result": {
        "id": "9f11c870-5616-49ad-b187-d93cbb100003",
        "status": { "state": "completed" },
        "artifacts": [
          {
            "parts": [
              { "kind": "text", "text": "Repeat after me: hello paywall" }
            ]
          }
        ]
      }
    }
    ```
  </Accordion>

  <Accordion title="Task get Request">
    ```json theme={null}
    {
      "jsonrpc": "2.0",
      "method": "tasks/get",
      "params": {
        "taskId": "9f11c870-5616-49ad-b187-d93cbb100003"
      },
      "id": "9f11c870-5616-49ad-b187-d93cbb100004"
    }
    ```
  </Accordion>
</AccordionGroup>

## Frontend Setup

```bash theme={null}
# Clone the Bindu repository
git clone https://github.com/GetBindu/Bindu

# Navigate to frontend directory
cd frontend

# Install dependencies
npm install

# Start frontend development server
npm run dev
```

Open [http://localhost:5173](http://localhost:5173) and try to chat with the echo paywall agent.