RingCentral APIs are designed to be used and tested directly in the production environment. There is no technical requirement for a separate sandbox or test environment in order to explore or integrate with the APIs.
If you'd prefer to isolate development activity, using a separate developer account is an option. Whether or not to do this is entirely up to your personal preference or your organization's policies. Some developers choose to create separate accounts for development and production use cases, while others use a single account for both.
This streamlined approach allows for faster iteration and eliminates the complexity and requirement of managing different environments for testing and production, unless you want to.
Historical Note
In December of 2024, RingCentral retired its developer sandbox environment. This change greatly simplified the process of producing an app. As a result of this change, the legacy concept of "app graduation" was retired.