What is essential for designing a REST API?

When designing a REST API, it is essential to have:

• Resources — clearly defined entities to which access is provided (e.g., users, products).
• Unique URIs for each resource, to identify and access them unambiguously.
• HTTP methods (GET, POST, PUT, DELETE, etc.) to perform operations on resources.
• HTTP response statuses so that the client understands the result of the request.

Without these elements, a REST API cannot function correctly, as they provide a standardized and predictable interface for interaction between the client and the server.