When dealing with APIs that handle multi-dimensional data, it's essential to focus Boundary Value Analysis on the boundary values of each dimension. This ensures thorough testing of the extremes, helping uncover potential issues related to data boundaries and interactions between dimensions. By examining boundary values, testers can enhance the robustness of the API in handling complex data scenarios.

Negative testing involves sending invalid types of data to check how well the API handles unexpected inputs. Valid data is used in positive testing, not negative testing.

The access token in OAuth is primarily meant to identify the user who authorized the application, allowing the application to access resources on behalf of that user. It does not necessarily identify the client or resource server.