Invoice Import from Excel

Hi, I cannot import correctly my excel files.
Every time an error is raised saying

Impossible to import the file because of :

The field name must be a string.

But for Excel, the cell is a string (with only number).

It seems to work if I add a letter but the import system is useless if I need to fake my data and correct them one by one once the import is done.

Do you have an idea how to fix it ?

Regards