There are field(s) which are not mapped to Entity Error in D365 import

 There are field(s) which are not mapped to Entity Error in D365 import

It is a common practice to use the export functionality to generate the entity template file that can be later used for imports. 

However, while exporting the template, in fixed width format with 'First row header' set to 'No' (in source data formats set up), the exported template will not have the column names. When this file is imported, it will result in this error.