Reactjs – I am sending JSON data from the Backend but when I am recieving the data on Frontend it is Showing text/html Data

I have developed Backend in NodeJS and Frontend in ReactJS. I have hosted the backend on my own pc. When I am accessing the Data from postman It is giving me JSON Data but when I am fetching the data on frontend, Api is giving html/text Data.

Frontend Code

class Auth {
    async fetchData() {
        try {
            const response = await fetch('/data/get-data', {
                method: 'GET',
                headers: {
                    'Content-Type': 'application/json'
                }
            });
            console.log("DEBUG : response", response); // Log the entire response object

            if (!response.ok) {
                throw new Error(`Failed to fetch data: Status code ${response.status}`);
            }

            const contentType = response.headers.get('content-type');
            if (!contentType || !contentType.includes('application/json')) {
                throw new Error('Unexpected content type: ' + contentType);
            }

            const jsonData = await response.json();
            console.log("DEBUG : jsonData", jsonData);
            return jsonData;
        } catch (error) {
            console.error('Error fetching data:', error);
            // Optionally handle errors gracefully on the frontend (e.g., display an error message)
        }
    }
}


const authService = new Auth();

export default authService

Backend Code

import { asyncHandler } from '../utils/asyncHandler.js';
import { ApiResponse } from '../utils/apiResponse.js';
import { Data } from '../models/data.model.js';
import { ApiErrors } from '../utils/ApiErrors.js';

const getData = asyncHandler(
    async (req, res) => {
        try {
            const data = await Data.find();

            console.log("nSuccessfully retrieved data...");
            res.setHeader('Content-Type', 'application/json');
            return res
                .status(200)
                .json(new ApiResponse(200, data,  "Data Sent Successfully!!"));
        } catch (error) {
            console.error('Error while fetching data:', error);
            const apiError = new ApiErrors(500, 'Internal Server Error');
            return res.status(apiError.statusCode).json(apiError);
        }
    }
);


export { getData };

Error

auth.js:25 Error fetching data: Error: Unexpected content type: text/html

I am new to MERN. Please help