Merx plugin. Complete order using Paypal not working

I am trying to use the Merx plugin for e-commerce, which I’ve managed to get it working apart from the final completion of payment through PayPal. In my checkout.php controller, I have the following.

<?PHP
 if (merx()->cart()->isEmpty()) {
  go('/');
 }
 if (kirby()->request()->method() === 'POST') {
  try {
  $data = $_POST;
  $redirect = merx()->initializePayment($data);
  go($redirect);
 } catch (Exception $ex) {
  echo $ex->getMessage();
  dump($ex->getDetails());
 }
}

and my config is:

<?php

use Kirby\Exception\Exception;

return [
  'debug' => true,
  'ww.merx.production' => false,
  'ww.merx.currency' => 'GBP',
  'ww.merx.currencySymbol' => '£',
  'ww.merx.gateways' => [
    'paypal' => [
      'ww.merx.paypal.sandbox.clientID' => '',
      'ww.merx.paypal.sandbox.secret' => ''
    ],
    'credit-card' => [
      'ww.merx.stripe.live.publishable_key' => 'pk_test_',
      'ww.merx.stripe.live.publishable_key' => 'sk_test_'
    ]
  ],
  'routes' => [
    [
      'pattern' => 'add',
      'method' => 'post|get',
      'action'  => function () {
        $id = get('id');
        $quantity = get('quantity');
        try {
          cart()->add([
            'id' => $id,
            'quantity' => $quantity,
          ]);
          go('/');
        } catch (Exception $ex) {
          return $ex->getMessage();
        }
      },
    ],
    [
      'pattern' => 'remove',
      'method' => 'post|get',
      'action'  => function () {
        $id = get('id');
        try {
          cart()->remove($id);
          go('/checkout');
        } catch (Exception $ex) {
          return $ex->getMessage();
        }
      },
    ],
  ],
  'hooks' => [
    'ww.merx.cart' => function ($cart) {
      if ($cart->count() > 0) {
        $cart->remove('shipping');
        if ($cart->getSum() < 2) {
          $cart->add([
            'id' => 'shipping',
          ]);
        }
      }
    }
  ],
];

I expected the go($redirect); to send to PayPal but instead, it loads the order.php of the order. Is there something / a setup step I’m missing?

Does anyone have experience with this plugin? Thanks for reading.

This question has already been posted. Please don’t post the same stuff twice. Closing this.

You might want to post your additional information in your original thread.