1. Understanding WooCommerce Payment Gateway Architecture

Customer → Checkout
    ↓
WC_Payment_Gateway::process_payment()
    ↓
Redirect / API Request
    ↓
Payment Provider
    ↓
Webhook Callback
    ↓
Order Status Update

• WooCommerce expects a structured response from process_payment().
• Order state management is critical (Pending → Processing → Completed).
• Session integrity must be maintained during redirection.
• Webhooks guarantee asynchronous confirmation.
• Security validation must occur before order completion.

2. Extending WC_Payment_Gateway Class

class WC_Custom_Gateway extends WC_Payment_Gateway {

  public function __construct() {
    $this->id = 'custom_gateway';
    $this->method_title = 'Custom Gateway';
    $this->has_fields = true;
  }

  public function process_payment($order_id) {
    $order = wc_get_order($order_id);

    return [
      'result'   => 'success',
      'redirect' => $this->get_return_url($order)
    ];
  }
}

• Extend WC_Payment_Gateway base class.
• Define unique gateway ID.
• Register admin settings fields.
• Implement process_payment() method.
• Return proper redirect array.

3. Secure Hashing & Checksum Validation (SHA-512)

$hash_string = $merchant_key . "|" . $txn_id . "|" . $amount . "|" . $secret;
$secure_hash = hash("sha512", $hash_string);

• Prevents request tampering.
• Validates integrity between merchant and gateway.
• Mandatory for PayU / Razorpay integrations.
• Secret key must never be exposed in frontend.

4. Handling Webhooks (IPN)

add_action('rest_api_init', function () {
  register_rest_route('custom/v1', '/webhook', [
    'methods'  => 'POST',
    'callback' => 'handle_webhook'
  ]);
});

• Registers custom REST endpoint.
• Processes asynchronous payment confirmations.
• Updates WooCommerce order status.
• Logs transaction for debugging.
• Ensures payment success even if user closes browser.

5. WooCommerce Blocks Compatibility

registerPaymentMethod({
  name: 'custom_gateway',
  label: 'Custom Gateway',
  content: ,
});

• Required for new React-based Checkout.
• Legacy PHP templates won't render in Blocks.
• Ensures future WooCommerce compatibility.

6. Deployment & Production Checklist

• Test in Sandbox Mode.
• Validate checksum logic.
• Whitelist webhook IPs.
• Enable logging during testing.
• Disable debug logs in production.
• Confirm refund callback handling.

7. Frequently Asked Questions