The Excel export/import format uses two rows for the column headers
As you see, there are two rows of headers before the issue rows start.
- The first row should show the issue fields with the names you use for them.
- The second row shows the internal names of these fields so that the files can be used for re-importing, assigning the values to the correct issue field.
The benefit of this is noticeable when using different languages, or using nonstandard names for the fields.
Compare these screenshots of sample Excel files (data taken from different projects, so not exactly the same fields):
Note that some fields have different names in these projects and languages. But the second row helps the system identify the correct issue field to import to.
This also means that to import issues from Excel, you should use the sample file, or an export as basis for the import file, so that you get this two-row column setup.