Eyeson is an online SaaS product where you need to register a user account online in order to use it for video meetings and group calls out of the box.
The eyeson API is for developers who want to implement their own business logic and processes and use only the live meeting part of eyeson. This works like that: you need to implement your own user accounts when using the API. The live part of eyeson needs only avatar and name to be displayed in the UI. All data and management and organization of data is your own implementation and eyeson do not provide support with that. If you need docs, coding examples and so on for API version, then follow this link.
Note, the eyeson API can only be accessed via an API key and it is a usage based model. In order to create and manage an API Key you need to signup on eyeson - so at least you need 1 licensed user on eyeson SaaS to start with an API key implementation. Check how to get your own API Key. The pricing for eyeson API differs from a simple eyeson licence.