List members lookup
Members lookup group has two available endpoints. You are able to retrieve details on members of a specified List and see which Lists a user is a member of. These endpoints can be used to enable people to curate and organize new Lists based on the membership information.
There is a rate limit of 900 requests per 15 minutes when looking up member details and a limit of 75 requests per 15 minutes when looking up user memberships.
Manage List members
The manage List members endpoints allow you to add and remove members to a List on behalf of an authenticated user. For these endpoints, there are two methods available: POST and DELETE. The POST method allows you to add a member to a List, and the DELETE method allows you to remove a member from a List. There is a user rate limit of 300 requests per 15 minutes for both endpoints.
Note that Lists cannot have more than 5,000 members.
Since you are making requests on behalf of a user with the these endpoints, you must authenticate them with either OAuth 1.0a User Context or OAuth 2.0 Authorization Code with PKCE, and use the user Access Tokens associated with a user that has authorized your App, which can be generated using the 3-legged OAuth flow (OAuth 1.0a) or the Authorization Code with PKCE grant flow (OAuth 2.0).