Unable to get the Payment_method_id using fetch API in stripe PaymentIntent

Question

I am using the PaymentIntent API to integrate Stripe payments using stripe-php SDK and Stripe.js V3. Following This guide https://stripe.com/docs/payments/payment-intents/migration#saving-cards-checkout. I am getting what successful payments in my Stripe Dashboard done with test cards which do not require 3d-secure. But The Stripe's new SCA 3d secure Popup(according to their docs.) is not popping up, Which leads payments done with 3dsecure ENABLED cards to "Incomplete Payments" Tab in stripe Dashboard.

I have examine the code thoroughly multiple times and tested. I have noticed that my code skips(somtimes) OR throws an error "Unexpected end of JSON input" in the "Fetch Part" on the client side code.. which leads the 3d-secure cards payments to be incomplete.The JavaScript Fetch function is not fetching the "payment_method_id" from the specified file(url).

My Payment.js File:

var elements = stripe.elements();
var style = {
    base: {
        color: '#32325d',
        lineHeight: '18px',
        fontFamily: '"Helvetica Neue", Helvetica, sans-serif',
        fontSmoothing: 'antialiased',
        fontSize: '16px',
        '::placeholder': {
            color: '#aab7c4'
        }
    },
    invalid: {
        color: '#fa755a',
        iconColor: '#fa755a'
    }
};

var cardNumber = elements.create('cardNumber', {
    style: style
});
cardNumber.mount('#cardNumber');
var cardExpiry = elements.create('cardExpiry', {
    style: style
});
cardExpiry.mount('#cardExpiry');
var cardCvc = elements.create('cardCvc', {
    style: style
});
cardCvc.mount('#cardCVC');

var cardholderName = $('#custName').val();
var amount = $('#amount').val();

$(document).ready(function () {
    $("#paymentForm").submit(function (event) {
        //event.preventDefault();

        stripe.createPaymentMethod('card', cardNumber, {
            billing_details: {name: cardholderName.value}
        }).then(function (result) {
            console.log(result);

            if (result.error) {
                var errorElement = document.getElementById('card-error');
                errorElement.textContent = result.error.massage;

            } else {
                 stripeTokenHandler(result);

                fetch('example.com/stripe/index.php', {
                    method: 'POST',
                    headers: {'Content-Type': 'application/json'},
                    body: JSON.stringify({
                        payment_method_id: result.paymentMethod.id
                    })
                }).then(function (result) {
                    // Handle server response (see Step 3)
                    result.json().then(function (result) {
                        handleServerResponse(result);
                    })
                });
            }
        });   
        //return false;
    });
 function stripeTokenHandler(result) {
            var payForm = $("#paymentForm");
            var paymentMethodID = result.paymentMethod.id;
            //set the token into the form hidden input to make payment
            payForm.append("<input type='hidden' name='payment_method_id' value='" + paymentMethodID + "' />");
            //  payForm.submit();   
             payForm.submit();
        }
}

My Index.php File

header('Content-Type: application/json');
if(isset($_POST['submit'])){

    //include Stripe PHP library
    require_once('stripe-php/init.php');    
   //set Stripe Secret Key
\Stripe\Stripe::setApiKey('sk_test_key');

    //add customer to stripe
    $customer = \Stripe\Customer::create(array(
        'email' => $custEmail,
    ));    

function generatePaymentResponse($intent) {
    if ($intent->status == 'requires_action' &&
        $intent->next_action->type == 'use_stripe_sdk') {
        # Tell the client to handle the action

        echo json_encode([
            'requires_action' => true,
            'payment_intent_client_secret' => $intent->client_secret
        ]);
    } else if ($intent->status == 'succeeded') {        
# The payment didn’t need any additional actions and completed!
        # Handle post-payment fulfillment
        echo json_encode([
            'success' => true
        ]);
    } else {
        # Invalid status
        http_response_code(500);
        echo json_encode(['error' => 'Invalid PaymentIntent status']);
    }
}
# retrieve json from POST body
  $json_str = file_get_contents('php://input');
  $json1 = json_encode($_POST);
  $json_obj = json_decode($json1);

  $intent = null;

try {
    if (isset($json_obj->payment_method_id)) {
    $intent = \Stripe\PaymentIntent::create([
    'payment_method' => $json_obj->payment_method_id,
    'customer' => $customer->id,
    'amount' => 1099,
    'currency' => 'gbp',
    'confirmation_method' => 'manual',
    'confirm' => true,

]);
}
    generatePaymentResponse($intent);

  }catch (\Stripe\Error\Base $e) {
    # Display error on client
    echo json_encode([
      'error' => $e->getMessage()
    ]);
  }


}
?>

As it can be seen my stripeTokenHandler is appending the payment_method.id into HTML form and the process goes on. but the "fetch" section of JS code should get payment_method_id to generate "Response" and to proceed for "next_action" if the payment status is "requires_action".

Answer 1

So, In order to achieve what i wanted to, what i did was

- removed stripeTokenHandler()

Because i was using it in my previous charges API integration and thought it will work with the new PaymentIntent. And i guess many people misunderstood or misguided buy bunch of different methods stripe has in its docs.I saw a lot of questions on internet people complaining that stripe's "poorly managed" Documentation has confused them.

- Learned Fetch Api.

As a newbie i didnt know what it was for.

- removed isset post submit from my php code

reason: payment.js was unable to POST the paymentMethod.id to the server using Fetch Api and get the response body back from the server to proceed the code further.

I MUST say that Stripe needs to improve its Docs about this SCA ready PaymentIntent thing.