aws_requests_auth problem

I'm trying to create an apigateway in order to create an api that integrates the lex bot. I did that using sam with lambda function;the probelm when I run locally my script using sam local start-api I got this :

Invalid lambda response received: Invalid API Gateway Response Keys: {'requestId', 'errorMessage', 'errorType', 'stackTrace'} in {'errorMessage': "Unable to import module 'app': No module named 'aws_requests_auth'", 'errorType': 'Runtime.ImportModuleError', 'requestId': 'XXXXXX', 'stackTrace': []} although I already installed aws_requests_auth lib and the api is working fine on postman.

I check the installation using pip list command and I got this : aws-requests-auth 0.4.3

this is the script :

import json import boto3 import os import uuid import requests from aws_requests_auth.aws_auth import AWSRequestsAuth

def run(event,context): URL = apiURL"

payload="{\r\n\r\n   \"text\": \"2012\"\r\n}"
#### put the  api-key found in the lapose.fr api documentation https://developer.laposte.fr/ 
headers = {

'Content-Type': 'application/json', 'X-Amz-Content-Sha256': 'XXXXXXXXX', 'X-Amz-Date': 'XXXXXXXXXXXX' } auth = AWSRequestsAuth( aws_access_key='XXXXXXXXXXX', aws_secret_access_key='XXXXXXXXXX', aws_host='runtime-v2-lex.us-east-1.amazonaws.com', aws_region='us-east-1', aws_service='lex' )

response = requests.post(URL, headers=headers, data=payload ,auth=auth)
print(response.json())


return{
  'statusCode':200,
  'headers': {
    'Content-Type': 'application/json',
    },
    'body': json.dumps(response.json())
    }