RMA state transitions
How state transitions are handled by the system.
The business logic can be injected by the merchant’s project through Litium State Transition Engine, by using the RmaState field.
RMA states
The following illustration shows how state transitions will be implemented by default:

Changes to Order State Machine
The Returned state in the existing Order State Machine will be removed and new states will be introduced, as shown in the illustration below. This is because an existing order should not be modified by putting it in Returned state. Instead, a new SRO should be created with its own states.

API testing
Please refer to this this article about API testing using the Postman development tool and request samples.