Amazon LEX throwing error while communicating with Lambda

I have been struggling to integrate a logic in LEX using lambda from the past 3 days and it keeps on throwing me the same error. I have read the AWS documentation for the Lex V2 and have (to the best of my ability) implemented the same in my response logic.The error message is as follows :

Invalid Lambda Response: Received invalid response from Lambda: Cannot construct instance of `IntentResponse`, problem: The validated object is null at [Source: (String)"{"dialogAction": {"type": "Close", "fulfillmentState": "Fulfilled"}, "intent": {"name": "Number_Route", "confirmationState": "Confirmed", "state": "Fulfilled"}, "messages": [{"contentType": "PlainText", "content": "Your number is: 123-456-7890"}]}"; line: 1, column: 245]

I tried this as my response format is :

answer = {"dialogAction": {"type": "Close","fulfillmentState": "Fulfilled",      },"intent": {"name": intent,"confirmationState": "Confirmed","state": "Fulfilled",      },"messages": [        {"contentType": "PlainText","content": f"Your number is: {formatted_number}",        }      ],    }    return answer

Thanks in advance