Oracle ' s microservices design guidance explicitly identifies responsive behavior, backward compatibility, flexible communication, and idempotency as important requirements. Flexible communication doesnotrequire every microservice to use one synchronous protocol. Oracle states that each microservice can specify the protocol used between clients and the API gateway as well as the protocol used between individual microservices. This flexibility supports loose coupling and allows synchronous or asynchronous communication where appropriate. Oracle also states that microservices should return a response even when the service fails, API changes should remain backward-compatible with existing clients, and repeated calls should produce the same outcome when idempotency is required. Consequently, option C directly contradicts Oracle ' s documented flexible-communication principle and is the NOT valid statement.