Integration Server 10.3 | Flat File Schema Developer's Guide | Working with Elements in Flat File Schemas and Dictionaries | Format Services | Working with Format Error Messages
 
Working with Format Error Messages
If the validate input variable of your format service was set to true to validate the format and value of a field, and that field does not meet the criteria specified in the service, you will receive an error message in the errorMessage output variable of the format service indicating why this field could not be validated.