AWS AppSync gives Unauthorized Access

session = requests.Session()
session.auth = AWS4Auth(
    # An AWS 'ACCESS KEY' associated with an IAM user.
    AWS_ACCESS_KEY_ID,
    # The 'secret' that goes with the above access key.                    
    AWS_SECRET,    
    # The region you want to access.
    AWS_REGION_NAME,
    # The service you want to access.
    'appsync'
)
# As found in AWS Appsync under Settings for your endpoint.
APPSYNC_API_ENDPOINT_URL = APPSYNC_ENDPOINT
# Use JSON format string for the query. It does not need reformatting.
query = """query MyQuery {
          getCustomer(id: "38c76f4f-c495-42e6-8599-647738a12692") {
            first_name
          }
        }"""
# Now we can simply post the request...
response = session.request(
    url=APPSYNC_API_ENDPOINT_URL,
    method='POST',
    json={'query': query}
)
print(response.text)

I want to be able to Read/Write data from AWS AppSync's dynamodb through python. I came across this solution online. But when I run it gives me the following error:

{
  "errors" : [ {
    "errorType" : "UnauthorizedException",
    "message" : "You are not authorized to make this call."
  } ]
}

I have given Administrator Access to the IAM User. What am I doing wrong here?