[Python] BItUnix API Signature Error (10007) when Placing order

BitUnix Futures API – Signature Error (code 10007)
​

I'm attempting to place a Futures order using BitUnix's REST API. Despite following the official documentation exactly, I consistently receive the error:

{
"code": 10007,
"data": null,
"msg": "Signature Error"
}


What I've done:

1. 
   Request URL and Method:
   POST https://fapi.bitunix.com/api/v1/futures/trade/place_order
   
   
2. 
   Headers:
   
   {
   "api-key": "my-api-key",
   "nonce": "random-hex-32-char",
   "timestamp": "in-milliseconds",
   "sign": "double-sha256 signature",
   "language": "en-US",
   "Content-Type": "application/json"
   }
   
   
   Payload (Minified):
   
   {
   "symbol": "BTCUSDT",
   "qty": "0.001",
   "side": "BUY",
   "tradeSide": "OPEN",
   "orderType": "MARKET"
   }
   
   
   Minimal Example:
   
   import hashlib, json, time, os, requests
   
   api_key = "your_api_key"
   secret_key = "your_secret_key"
   
   payload = {
   "symbol": "BTCUSDT",
   "qty": "0.001",
   "side": "BUY",
   "tradeSide": "OPEN",
   "orderType": "MARKET"
   }
   body = json.dumps(payload, separators=(",", ":"))
   
   nonce = os.urandom(16).hex()
   timestamp = str(int(time.time() * 1000))
   
   digest_input = nonce + timestamp + api_key + "" + body
   first_hash = hashlib.sha256(digest_input.encode()).hexdigest()
   signature = hashlib.sha256((first_hash + secret_key).encode()).hexdigest()
   
   headers = {
   "api-key": api_key,
   "nonce": nonce,
   "timestamp": timestamp,
   "sign": signature,
   "language": "en-US",
   "Content-Type": "application/json"
   }
   
   res = requests.post(
   "https://fapi.bitunix.com/api/v1/futures/trade/place_order",
   headers=headers,
   data=body
   )
   
   print("Status:", res.status_code)
   print("Response:", res.text)
   
   
   Official Documentation:
   https://openapidoc.bitunix.com/doc/common/introduction.html
   

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