authentication conditions for using the API

We will change Acrobat Pro 2020 to Acrobat Pro latest version.
To use the latest version, the user to whom the license is assigned must log in and be authenticated.
However, when users use Acrobat API need not log in and be authenticated.
We are using Acrobat API to get transparent text, optimize files, and merge multiple files.

We got all 2,3,4 pattern. we does not try 1 pattern.

1. User is not authenticated, API not available.
2. User is not authenticated, API available.
3. User is authenticated, API not available.
4. User is authenticated, API available.

Why does this phenomenon occur?
Please let us know what are the authentication conditions for using the API?