Using blocks lookup, you can see who you or an authenticated user has blocked. This can be useful for determining how you can interact with a given account.
The blocks lookup GET endpoint allows you to see which accounts you’ve blocked on behalf of an authorized user. This endpoint has a rate limit of 15 requests per 15 minutes per user.
Since you are making requests for private information with blocks lookup, and on behalf of a user with manage blocks, you must authenticate these endpoints 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).