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

# Nevermined x402 and Google AP2

> Run the ADK demo to combine Nevermined x402 payments with Google AP2/A2A messaging—covering session tokens, facilitator verify/settle, and AP2 payment intents.

This guide shows how the ADK demo wires Nevermined x402 payments into Google AP2/A2A messaging. It reuses the core primitives (plan + agent + session token + facilitator) and transports them over AP2 messages between a client agent and a merchant server. Source: [ADK demo README](https://github.com/nevermined-io/a2a-x402/tree/feat/a2a-nvm/python/examples/adk-demo#readme).

## What this covers

* Uses the `python/examples/adk-demo` from `a2a-x402` ([demo repo](https://github.com/nevermined-io/a2a-x402/tree/feat/a2a-nvm))
* Client agent (subscriber) generates x402 session tokens
* Merchant server verifies and settles via Nevermined facilitator over REST
* AP2 carries `payment-required` and `payment-submitted` messages between agents
* Real on-chain credit burns on Base Sepolia (sandbox)

## Prerequisites

* Nevermined API keys: one for the merchant (`NVM_API_KEY_SERVER`), one for the subscriber (`NVM_API_KEY_CLIENT`)
* A credits plan and agent registered in Nevermined (`NVM_CREDITS_PLAN_ID`, `NVM_AGENT_ID`)
* Python 3.11+, `uv` (for the demo env)
* Google GenAI API key (for the AP2/ADK flow)

## Configure the demo

From the root of `a2a-x402`:

```bash theme={null}
uv sync --directory=python/examples/adk-demo
cp python/examples/adk-demo/.env.sample python/examples/adk-demo/.env
```

Set the key environment variables (sandbox defaults):

```bash theme={null}
NVM_API_KEY_SERVER="nvm:merchant-jwt"
NVM_API_KEY_CLIENT="nvm:subscriber-jwt"
NVM_ENVIRONMENT="sandbox"
NVM_CREDITS_PLAN_ID="your-plan-id"
NVM_AGENT_ID="your-agent-id"
NVM_PAYMENT_AMOUNT="2"
NVM_NETWORK="base-sepolia"
GOOGLE_GENAI_API_KEY="your-google-api-key"
```

Key roles (from the README):

* **Client Agent (subscriber)**: Generates x402 session tokens using `payments_py`.
* **Merchant Server (agent)**: Serves AP2 `payment-required`, verifies/settles via Nevermined facilitator.
* **Facilitator**: Nevermined service that enforces permissions and burns/orders credits.
* **Blockchain**: Executes the settlement transactions (Base Sepolia in sandbox).

## Run it

1. Start the merchant server (facilitator + AP2 handler):

```bash theme={null}
uv --directory=python/examples/adk-demo run server
```

2. Start the client agent + web UI:

```bash theme={null}
uv --directory=python/examples/adk-demo run adk web --port=8000
```

3. In the UI, trigger a purchase (e.g., “buy a laptop”). The flow:

* Merchant replies with AP2 `payment-required` (plan/agent/amount/network)
* Client **generates x402 session token** via Nevermined (`payments_py.x402.get_x402_access_token`)
* Client sends `payment-submitted` carrying the x402 payload + Nevermined extension
* Merchant **verifies** with facilitator → does the work → **settles** (burns credits)
* Response includes receipt + transaction hash; balance decrements (e.g., 10 → 8)

## Message shapes (adapted from the README)

* `payment-required`:
  * Includes plan\_id, agent\_id, amount, network, scheme, and any metadata the merchant wants to expose.
* `payment-submitted`:
  * Carries the x402 payload with `session_key` plus the copied Nevermined extension.
* `payment-completed`:
  * Contains the facilitator’s verification/settlement result and transaction hash.

## Key SDK touchpoints

* Session token generation (subscriber):

```python theme={null}
from payments_py.x402 import X402TokenOptions, DelegationConfig, CreateDelegationPayload

# Create a delegation once, then reuse its id to mint tokens.
delegation = payments.delegation.create_delegation(
    CreateDelegationPayload(
        provider="erc4337",  # "stripe" | "braintree" | "visa" for fiat plans
        spending_limit_cents=10000,  # $100 budget
        duration_secs=604800,  # 7 days
        currency="usdc",  # "usd" for fiat plans
    )
)
token_res = payments.x402.get_x402_access_token(
    plan_id,
    agent_id,
    token_options=X402TokenOptions(
        delegation_config=DelegationConfig(delegation_id=delegation.delegation_id)
    ),
)
session_key = token_res["accessToken"]
```

* Facilitator verification + settlement (merchant):

```python theme={null}
verification = payments.facilitator.verify_permissions(
    payment_required=payment_required,
    x402_access_token=access_token,
)
if not verification.is_valid:
    raise Exception("Payment Required")

payments.facilitator.settle_permissions(
    payment_required=payment_required,
    x402_access_token=access_token,
)
```

## When to use this pattern

* You need AP2/A2A messaging but want enforceable on-chain payments
* You want to keep REST facilitators for verification/settlement while agents talk over AP2
* You need a working reference with real settlement (Base Sepolia) that mirrors the library E2E tests

## Links

* Demo repo: [https://github.com/nevermined-io/a2a-x402/tree/feat/a2a-nvm](https://github.com/nevermined-io/a2a-x402/tree/feat/a2a-nvm)
* Demo README: [https://github.com/nevermined-io/a2a-x402/tree/feat/a2a-nvm/python/examples/adk-demo#readme](https://github.com/nevermined-io/a2a-x402/tree/feat/a2a-nvm/python/examples/adk-demo#readme)


## Related topics

- [Nevermined x402](/docs/development-guide/nevermined-x402.md)
- [x402 Facilitator Overview](/docs/products/x402-facilitator/overview.md)
- [Monetize Your AI](/docs/solutions/agent-to-agent-monetization.md)
- [How the x402 Facilitator Works](/docs/products/x402-facilitator/how-it-works.md)
- [Payment Models](/docs/integrate/patterns/payment-models.md)