Hey Andriana,
first of all, thank you for the purchase!
Please check that you are uploading the archive called “Sensei_Installable.zip” which is located inside the “Sensei_WP_Theme_Package” folder, which in turn is obtained by unzipping the main ThemeForest archive (as per the instructions provided on page 1 of the theme manual. Please let me know if you are uploading the mentioned file (“Sensei_Installable.zip”) and the problem still persists.
Sincerely,
Andrii / Satori Studio