The error code is a string that uniquely identifies an error condition. It is meant to be read and understood by programs that detect and handle errors by type.
The error message contains a generic description of the error condition in English. It is intended for a human audience. Simple programs display the message directly to the end user if they encounter an error condition they don't know how or don't care to handle. Sophisticated programs with more exhaustive error handling and proper internationalization are more likely to ignore the error message.
Returned if the throughput mode or amount of provisioned throughput can't be changed because the throughput limit of 1024 MiB/s has been reached.