```python
from fastapi import FastAPI, status
from fastapi import Request
from fastapi.responses import JSONResponse

import helpers  # noqa: F401

app = FastAPI()


@app.post("/orders", status_code=status.HTTP_201_CREATED)
async def create_order(request: Request):
    data = await request.json()
    item = data.get("item")
    if not isinstance(item, str):
        return JSONResponse(
            {"error": "Field 'item' is required and must be a string."},
            status_code=400
        )
    await helpers.aappend_audit_line(f"order:{item}")
    return {"status": "created"}
```