Implement configuration, checkout, callbacks and refunds safely.

Structure and class

modules/gateways/acmepay/acmepay.php    // class AcmepayGateway
modules/gateways/acmepay/callback.php

<?php
class AcmepayGateway {
 public function meta(): array { return ['DisplayName'=>'Acme Pay','SupportsRefunds'=>true]; }
 public function getConfigFields(): array { return [
  'name'=>['FriendlyName'=>'Display Name','Type'=>'text','Default'=>'Acme Pay'],
  'api_key'=>['FriendlyName'=>'API Key','Type'=>'password']
 ]; }
 public function testConnection(array $config): array { return ['success'=>true,'message'=>'Connected']; }
 public function renderPaymentButton(array $invoice,array $config): string { /* hosted checkout */ return ''; }
 public function refundTransaction(array $params,array $config): array { return ['success'=>false,'message'=>'Not implemented']; }
}

Callback checklist

1. Load bootstrap and read raw input once.
2. Verify provider signature and timestamp first.
3. Resolve invoice, transaction ID, amount, fee and currency.
4. Call Gateway::processVerifiedPayment($invoiceId,$txnId,$amount,$fee,'acmepay',$currency).
5. Return the provider-required status without exposing internal errors.

The current release also requires adding gateway metadata to Gateway::getGatewayRegistry().