Merge's Unified API facilitates the integration of over 180 services, including HRIS platforms like Gusto, by allowing developers to incorporate multiple integrations into their products through a single API. Gusto offers a comprehensive HR management system with features such as payroll, benefits, and time tracking, accessible via an API that developers can use to integrate HR data into other business applications. To connect with the Gusto API, developers must implement OAuth 2.0 authentication, obtain authorization codes, and exchange them for access tokens, which are used to authenticate API requests. The Merge Unified API simplifies managing these integrations by using a centralized endpoint and plugin system to communicate with various platforms, reducing the need for individual integrations and streamlining the development process. This approach allows developers to focus on enhancing their core products while leveraging the unified system to access and manage data across multiple HRIS platforms efficiently.