Optional. Contains the error message returned by the server. If empty or not present, that signals that the upload request has been completed successfully.
If not empty, the error message can indicate the following error scenarios:
Thru Server exception
The Thru server explicitly raised an exception due to a violation of business/data rules or constraints in the system.
An exception was raised by the system due to an unknown reason. The error message will have the following structure: 90000 / Message