```python
from fastapi import FastAPI, Depends, status
import asyncio
import helpers

app = FastAPI()

billing = helpers.BillingClient()  # the shared client instance


def get_billing() -> helpers.BillingClient:
    """FastAPI dependency providing the billing client."""
    return billing


@app.post("/charges", status_code=status.HTTP_201_CREATED)
async def create_charge(
    amount: float, billing_client: helpers.BillingClient = Depends(get_billing)
):
    """Charge the amount and return the receipt."""
    receipt_id = await asyncio.to_thread(billing_client.charge, amount)
    return {"receipt": receipt_id}
```