An API is a software interface that allows two applications to communicate with each other. Simply put, the messenger submits a request to a provider, after which the provider provides feedback. Verifai offers Software Development Kits (SDKs) consisting of multiple APIs. While an API is built specifically to perform a specific function, namely enabling communication between applications, an SDK is an integrated platform that has a set of tools to create these applications. APIs allow interaction between applications, but they are not in themselves sufficient to create a brand new application.
In conclusion you can say that Verifai indeed offers APIs, but goes a step further by also offering the tools to realize ID verification.