How to get api_access_point when using oauth/v2 API?

I created a new API Application (the other one I had was more than a year old).
When using the new application, I need to use the oauth/v2 endpoint. (For the old application, the old endpoint still works).
When redirecting to return the authorization code, the api_access_point parameter is not returned (the old API returns it).

Actual behavior: like https://opensource.adobe.com/acrobat-sign/developer_guide/helloworld.html#success-vs-failure

Expected behavior: like https://opensource.adobe.com/acrobat-sign/developer_guide/helloworld.html#the-customer-experience

How am I supposed to retrieve the api_access_point parameter?
- The basicUris endpoint requires authentication, so this is a chicken and egg problem.
- Also the design of https://opensource.adobe.com/acrobat-sign/developer_guide/helloworld.html#getting-the-access-token is weird. I need to know the api_access_point to call it. How does it help that it is returned by the function?

Thank you