Add testnet faciliator to docs

Author: janewang

docs/build/apps/x402.mdx

@@ -20,18 +20,33 @@ To support x402 on Stellar, a wallet must support [auth-entry signing](../guides
 - Hana
 - HOT
 - Klever
-- One Key
+- OneKey
 
 :::note
 
 Freighter Mobile does not currently support x402; use the Freighter browser extension. Mobile support is planned for a future release.
 
 :::
 
-## x402 Facilitator from OpenZeppelin
+## x402 Facilitator
 
 The [OpenZeppelin Relayer x402 Plugin for x402](https://github.com/OpenZeppelin/relayer-plugin-x402-facilitator) implements the x402 facilitator API so you can serve x402 payments directly from a Relayer instance. It works with the Coinbase x402 ecosystem (e.g., @x402/express) and exposes the expected `/verify`, `/settle`, and `/supported` endpoints under the Relayer plugin router.
 
+### Facilitator Service
+
+The x402 Facilitator Service is now live. Under the hood, the plugin leverages OpenZeppelin Channels to submit transactions onchain via a managed Relayer and Facilitator setup.
+
+#### Testnet Facilitator
+
+To use the deployed x402 plugin on testnet, you will need:
+
+- An API Key (Relayer Service). Generate your testnet API key here: https://channels.openzeppelin.com/testnet/gen
+- Facilitator URL. Use the following facilitator endpoint in your configuration: `https://channels.openzeppelin.com/x402/testnet`
+
+#### Mainnet Facilitator
+
+Coming soon.
+
 :::note
 
 This version supports x402 v2 specification. For x402 v1 support, please use a previous version of this plugin (check git history for v1 compatible releases).