OTPay WooCommerce – Custom WordPress Payment Gateway Plugin & Backend Integration

Custom WooCommerce payment gateway plugin for OTPay, built with WordPress and PHP, enabling secure payment processing integration between WooCommerce and external payment systems through a custom backend communication layer.

Overview

This project involved building a custom WooCommerce payment gateway plugin for OTPay, enabling seamless payment processing integration between a WordPress-based e-commerce system and an external payment infrastructure.

The solution extends WooCommerce’s native payment system with a fully custom plugin layer, allowing secure transaction flow, order synchronization, and backend communication with the OTPay payment service.

🧩 Project Scope

Key responsibilities included:

• Development of a custom WooCommerce payment gateway plugin
• Integration of external payment provider (OTPay) into WordPress checkout flow
• Secure handling of payment requests and responses
• Order status synchronization via backend callbacks/webhooks
• Implementation of secure API communication between WooCommerce and OTPay backend
• Ensuring compatibility with WooCommerce checkout lifecycle

🧰 Technology Stack

• CMS: WordPress
• E-commerce Engine: WooCommerce
• Backend Language: PHP
• Plugin Type: Custom WooCommerce Payment Gateway
• Communication Layer: REST API / Webhooks
• Database: MySQL
• Server Layer: NGINX on Linux infrastructure
• Architecture Style: Plugin-based payment integration system

⚙️ Key Features

💳 Custom WooCommerce Payment Gateway

Built a fully custom payment method that integrates directly into WooCommerce checkout, allowing customers to complete payments through OTPay.

🔐 Secure Payment Flow

Implemented secure transaction handling between:

• WooCommerce checkout session
• OTPay external payment system
• Backend callback verification layer

Ensured order integrity and prevented unauthorized payment state changes.

🔄 Webhook-Based Order Synchronization

Developed a callback mechanism to update WooCommerce order status based on real-time payment events from OTPay.

🧠 Plugin Architecture Design

The plugin follows WooCommerce standards:

• Extends WooCommerce payment gateway class
• Modular and maintainable structure
• Configurable settings from WordPress admin panel
• Secure API key management

🏗 System Architecture

The system follows a 3-layer payment integration model:

• Frontend Layer (WooCommerce Checkout) → Customer initiates payment flow

• Plugin Layer (WordPress Custom Gateway) → Handles request transformation and API communication

• Payment Provider Layer (OTPay Backend) → Processes payment and returns transaction status via webhook

🚧 Challenges & Solutions

🔄 Payment State Synchronization

Ensuring WooCommerce order status matched external payment provider status in real time.

Solution: Implemented webhook-based callbacks to synchronize payment state updates reliably.

🔐 Secure API Communication

Preventing unauthorized requests and ensuring secure transaction validation.

Solution: Introduced request signing / token-based validation between WooCommerce and OTPay backend.

⚙️ WooCommerce Compatibility

Ensuring smooth integration with WooCommerce checkout lifecycle without breaking existing payment methods.

Solution: Followed WooCommerce gateway abstraction standards and tested across multiple checkout flows.

📌 Outcome

The final system successfully enabled WooCommerce stores to process payments through OTPay using a fully custom plugin architecture, providing a secure, extensible, and production-ready payment integration layer.

💬 Note

This project demonstrates advanced WordPress engineering beyond theme development, focusing on:

• Custom payment gateway architecture
• WooCommerce plugin development
• Secure backend communication systems
• Payment workflow integration design
• Production-grade e-commerce system extension

🔗 Project

• Website: https://otpay.com.ua/