Im using request python to call api from AE-Affiliate Aliexpress. But got error “The request signature does not conform to platform standards”

This is the code that I used for requesting API

def generatesign(api_name,appSecret,params):
    parameters=[]
    for key,value in params.items():
        if key=="sign":
            continue
        if len(value)>0:
            parameters.append(key+value)
            parameters=sorted(parameters)
    if "/" in api_name:
         concatenated=api_name+"".join(parameters)
    else:
         concatenated = "".join(parameters)
    sig = hmac.new(appSecret.encode(), concatenated.encode(), hashlib.sha256)
    return sig.hexdigest().upper(),concatenated
time_stamp = str(int(time.time() * 1_000_000))

params2 = {
    'access_token': 'my_acess_token',
    'app_key': 'my_appkey',
    'format': 'json',
    'method': 'aliexpress.ds.freight.query',
    'partner_id': 'iop-sdk-python-20220609',
    'queryDeliveryReq': '{"productId":"3256806253680321","selectedSkuId":"12000037172759189","quantity":1,"shipToCountry":"US","source":"","currency":"","language":"","locale":"EN"}',
    'session': 'my_acess_token',
    'sign_method': 'sha256',
    'simplify': 'false',
}
sign,check=generatesign("https://api-sg.aliexpress.com/sync?","MhCSYFLKUxp4gd0NvryILtoc6XlT76IN",params2)
params2["sign"]=sign
params2['timestamp']=time_stamp
response = requests.post('https://api-sg.aliexpress.com/sync?', params=params2,cookies=cookies, headers=headers)

But I give me an error IncompleteSignature.
I want response like this

{
    "aliexpress_ds_freight_query_response": {
        "result": {
            "msg": "Item is not allowed to this country",
            "code": 602,
            "success": false
        },
        "request_id": "210126da17235447546796602"
    }
}