Having an issue with Lambda response that LexBot expect.

I have a lambda which query dynamo Db table for an available times once the the date is entered by the user and then the lambda will add those available time to the session attribute and will elicit to next slot. but once the user entered the date then the lex gives me an error message which I believe is about the response from the lambda. here is the lex error message

Invalid Lambda Response: Received invalid response from Lambda: Cannot construct instance of `java.util.LinkedHashMap` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('slots') at [Source: (String)"{"sessionState":{"sessionAttributes":{"availableTimes":"2:30 PM, 8:00 AM"},"intent":{"name":"Date","slots":"slots"}},"dialogAction":{"type":"ElicitSlot","fulfillmentState":"Fulfilled","slotToElicit":"Time","message":{"contentType":"PlainText","content":"What time would you like to schedule your appointment?"}}}"; line: 1, column: 108]

here is the lambda code

import { DynamoDBClient, QueryCommand } from "@aws-sdk/client-dynamodb";
import { unmarshall } from "@aws-sdk/util-dynamodb";

const REGION = "us-east-1";
const dynamodbClient = new DynamoDBClient({ region: REGION });

export const handler = async (event) => {
    console.log("EVENT: ", JSON.stringify(event, null, 2));

    try {
        const sessionState = event.sessionState || {};
        const intent = sessionState.intent || {};
        const slots = intent.slots || {};
        const dateSlot = slots.Dates || {};
        const appointmentDate = dateSlot.value ? dateSlot.value.interpretedValue : null;
        const params = {
            TableName: "Schedule",
            KeyConditionExpression: "availableDates = :date",
            ExpressionAttributeValues: {
                ":date": { S: appointmentDate }
            }
        };
        const command = new QueryCommand(params);
        const response = await dynamodbClient.send(command);

        const items = response.Items.map((item) => unmarshall(item));
        console.log('Data from Schedule: ', items);

        let availableTimesSet = new Set();
        items.forEach(item => {
            if (item.availableTimes) {
                availableTimesSet.add(item.availableTimes);
            }
        });
        const availableTimesArray = Array.from(availableTimesSet);
        const availableTimes = availableTimesArray.join(', ');

        sessionState.sessionAttributes = sessionState.sessionAttributes || {};
        sessionState.sessionAttributes.availableTimes = availableTimes;
        return {
            sessionState: {
                sessionAttributes: sessionState.sessionAttributes || {},
                intent: {
                    name: "Date"
                }
            },
            dialogAction: {
                type: "ElicitSlot",
                fulfillmentState: "Fulfilled",
                slotToElicit: "Time",
                message: {
                    contentType: "PlainText",
                    content: "What time would you like to schedule your appointment?"
                }
            }
        };
    }
    catch (error) {
        console.error('Error querying DynamoDB', error);
        return {
            sessionAttributes: event.sessionState ? event.sessionState.sessionAttributes : {},
            dialogAction: {
                type: "Close",
                fulfillmentState: "Failed",
                message: {
                    contentType: "PlainText",
                    content: `There was an error retrieving available times. Please try again later.`
                }
            }
        };
    }
};

I need help with processing the lambda response according to the lex requirement PS: I have read too many documents