"Check that the mapping for this import matches with the field names in the import file." during a sales order import.

During a sales order import from a flat file, if you receive the error "Check that the mapping for this import matches with the field names in the import file." it is typically caused by a change in the file's columns or column names.

When performing a sales order import (File> Import Sales Orders), if the error "Check that the mapping for this import matches with the field names in the import file" is received, it's typically due to a change in the file and the sales order import mappings need to be updated as well.

For example, if you have a column named "OrderQty" and you map that to the Quantity Ordered field in the Import Sales Order window and then you later you change the field name in the file to "Qty Ordered", you will receive the error. 

This is because the mapping was saved with the column name "OrderedQty", but that column header no longer exist, it's now "Qty Ordered".

To fix, edit your import mappings and check each mapped column. You may need to use the drop down to reselect the column name.