问为什么我在腾讯会议API中不断收到错误代码400？

{'Content-Length': '0', 'Accept-Encoding': 'gzip, deflate', 'X-TC-Timestamp': '1589787785', 'X-TC-Nonce': '243222', 'User-Agent': 'python-requests/2.23.0', 'X-TC-Key': 'xxx', 'Connection': 'keep-alive', 'Accept': 'application/json', 'AppId': '200000164', 'content-type': 'application/json', 'X-TC-Signature': 'ZmUzYjg4ZjRlNTIwYTRiYTlhZGY3YTVhMzBiZGU4YjM3MDBhYWRmMmQ4OGJkYWE1NWQ2NmIzMjQ2ODQyNDkyNQ=='}

def add(start,end):

    uri = '/v1/meetings'
    userid = User.id
    settings = {
            "mute_enable_join" : True,
            "allow_unmute_self" : True,
            "mute_all" : False,
            "host_video" : False,
            "participant_video" : False,
            "enable_record" : False,
            "play_ivr_on_leave" : False,
            "play_ivr_on_join" : False,
            "live_url" : False
    }
    params = {'userid':userid,'instanceid': 5,
              'subject':'consultation','type':0,
              'start_time':str(start),
              'end_time':str(end),
              'settings':str(settings)}
    headers = generateHeaders('POST',params,uri)

    response = requests.post("https://api.meeting.qq.com/v1/meetings",headers=headers,params=params)
    print(response.request.headers)
    print(response.url)
    return response.json()

def generateHeaders(method,params,uri):
    nonce = generate_nonce()
    timeStamp = int(time.time())

    headerString = "X-TC-Key=" + SecretId + "&X-TC-Nonce=" + str(nonce) + "&X-TC-Timestamp=" + str(timeStamp)
    stringSign= method+"\n"+str(headerString)+"\n"+uri+"\n"+str(params)
    b64 = create_sign(SecretKey,stringSign)

    print('final=',b64)

    return {'X-TC-Key': SecretId,
            'X-TC-Timestamp': str(timeStamp),
            'X-TC-Nonce': str(nonce),
            'AppId': str(appID),
            'X-TC-Signature': str(b64),
            'content-type':'application/json',
            'Accept': 'application/json'}

def create_sign(key,toSign):


    h = hmac.new(key,msg=toSign.encode('utf-8'),digestmod=hashlib.sha256).hexdigest()
    print(type(h))
    print(h)
    base = base64.b64encode(h.encode('utf-8'))
    hash = base.decode('utf-8')
    return hash