Will a plugin that creates a notice above the theme upload to extract the ZIP first help?
Although instead of telling the buyer to install that plugin, it will be easier to tell the buyer to extract the ZIP ..
Thank you very much. I learned with a friend how to access my ftp (did not know how to) and installed the theme in putting the folder (not the zip one this time) in the wp-content / theme folder. It then worked
I still don’t know why it did not work through the automatic installation through wordpress but at least I have my new theme.
Thanks again for helping!