Developers

// functions.php
add_action('wp_ajax_create_checkout', function() {
    $response = wp_remote_post(
        'https://creativemark.co/api/v1/stores/your-store/checkout/external-cart/',
        [
            'headers' => [
                'Authorization' => 'Bearer ' . EPAY_API_KEY,
                'Content-Type' => 'application/json',
                'X-Idempotency-Key' => wc()->cart->get_cart_hash(),
            ],
            'body' => json_encode([
                'customer' => [
                    'email' => wp_get_current_user()->user_email,
                    'name' => wp_get_current_user()->display_name,
                ],
                'items' => array_map(function($item) {
                    $product = $item['data'];
                    return [
                        'sku' => $product->get_sku(),
                        'name' => $product->get_name(),
                        'quantity' => $item['quantity'],
                        'unit_price_minor' => (int) round($product->get_price() * 100),
                    ];
                }, wc()->cart->get_cart()),
                'currency' => 'GBP',
            ]),
        ]
    );
    wp_send_json(json_decode(wp_remote_retrieve_body($response)));
});

// Node.js / Express
app.post('/buy', async (req, res) => {
  const resp = await fetch(
    'https://creativemark.co/api/v1/stores/your-store/checkout/external-cart/',
    {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${API_KEY}`,
        'Content-Type': 'application/json',
        'X-Idempotency-Key': req.body.cartId,
      },
      body: JSON.stringify({
        customer: req.body.customer,
        items: req.body.items,
        currency: 'GBP',
        presentation: 'embedded',
      }),
    }
  );
  const { payment_url } = await resp.json();
  res.redirect(payment_url);
});

<!-- Single product -->
<a href="https://creativemark.co/s/your-store/cart/?add=SKU-001&currency=GBP">
  Buy Now
</a>

<!-- Multiple products -->
<a href="https://creativemark.co/s/your-store/cart/?items=SKU1:1,SKU2:2&currency=GBP">
  Buy Bundle
</a>