Hello maartenv,
Thanks for the answer !
I don't have access to the WordPress site, the only thing I have is the backup file that my friend send me. I can ask him to tell the dev to send a new file but for that, I need to be sure the problem is not from my side. This is why I would like to be...
So I have received a word-press backup file from a friend who wants to change of dev because he had some problems with the actual one.
So he asks him to get a backup file before telling him in case the dev deletes everything because he will be mad.
(I never used Plesk and word-press before but...