-2011 Unknown order sent. Error for Cancel All Open Orders on a Symbol endpoint

I have two open orders on Spot Test Network opened with API calls. I’m trying to cancel them with Cancel All Open Orders on a Symbol endpoint. I provide all the params required, but I keep getting an -2011 error response:

{
    "code": -2011,
    "msg": "Unknown order sent."
}

My params:

symbol: BTCUSDT
timestamp: {{timestamp}}
signature: {{signature}}

My call. cURL:

curl --location --request DELETE 'https://testnet.binance.vision/api/v3/openOrders?symbol=BTCUSDT&timestamp=1595241326879&signature={SIGNATURE}' \
--header 'Content-Type: application/json' \
--header 'X-MBX-APIKEY: {YOUR_API_KEY}'

Why? What’s wrong with the request? How to fix?

If the order status is not NEW (open order), this message will be returned. I would suggest to query the order status by GET /api/v3/orderand confirm the order status.