If an issued command or message could not be applied, an appropriate error response conveys this information back to the issuer. Failure of a command or message can have various reasons, starting from missing permissions to internal server errors during processing of the command.
The Ditto Protocol for Errors defines how error responses look in Ditto Protocol.
An overview of all Thing-related error responses can be found in the examples chapter “Error responses” of the Ditto Protocol.