index.js

buyButton.addEventListener('click', async (event) => {

            const response = await fetch('/order', {
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json'
                },
                body: JSON.stringify({ amount: 500 }) // Rs.500
            });

            const responseJson = await response.json();

            const { order } = responseJson;

            const razorPayOptions = {
                key: '<YOUR_KEY_ID_HERE>',
                amount: 500,
                currency: 'INR',
                name: `Buy Shirt`,
                description: `Paying for testing`,
                order_id: order.id,
                handler: function (response) { // handler function when payment is successfull
                    const razorpayPaymentId = response['razorpay_payment_id'];
                    const razorpayOrderId = response['razorpay_order_id'];
                    const razorpaySignature = response['razorpay_signature'];

                    console.log('Payment successfull');
                },
            };

            const razorpayInstance = new Razorpay(razorPayOptions);
            razorpayInstance.open();

        });