PAY.JP is a payment API from PAY Inc. designed for developers building web and mobile applications. It lets businesses accept credit cards, Apple Pay, and recurring payments through a RESTful API with server-side libraries for Python, Ruby, PHP, Java, Node.js, Perl, and Go.

The service holds PCI DSS Version 4.0 Level 1 Service Provider certification and uses tokenization to prevent merchants from handling card data directly. It offers competitive transaction fees with volume-based pricing, and provides platform business features that support marketplaces, sharing economy services, and multi-tenant e-commerce operations.

The service supports 3D Secure authentication to add cardholder verification during card transactions, helping reduce fraud and meet security requirements.

Developers integrate payment processing through a modern REST API with JSON responses and comprehensive server-side libraries, enabling custom implementations with straightforward code.

API documentation and technical reference materials are available in English to support international developers working in Japan.