Pass the async client to x402ResourceServer for FastAPI. Pass the sync client to x402ResourceServerSync for Flask.

pip install cryptonly-x402 "x402[fastapi,evm]"

x402 >=2 is a dependency. Install the extra for the framework and chain you use, such as x402[fastapi,evm] or x402[flask,evm].

import os

from cryptonly_x402 import CryptonlyFacilitatorClient
from x402.mechanisms.evm.exact import ExactEvmServerScheme
from x402.server import x402ResourceServer

facilitator = CryptonlyFacilitatorClient(os.environ["CRYPTONLY_API_KEY"])

server = x402ResourceServer(facilitator)
server.register("eip155:8453", ExactEvmServerScheme())

api_key is your Cryptonly API key. It is sent as x-tenant-api-key on verify, settle, and supported.

facilitator = CryptonlyFacilitatorClient(os.environ["CRYPTONLY_API_KEY"])

Flask uses the sync client:

from cryptonly_x402 import CryptonlyFacilitatorClientSync
from x402.mechanisms.evm.exact import ExactEvmServerScheme
from x402.server import x402ResourceServerSync

facilitator = CryptonlyFacilitatorClientSync(os.environ["CRYPTONLY_API_KEY"])

server = x402ResourceServerSync(facilitator)
server.register("eip155:8453", ExactEvmServerScheme())

Set sandbox=True to use the sandbox facilitator with testnest.