I am trying to upload a zip file (of Avone theme - from themeforest.net).
I get the following message:
Go redownload the zip and try again.
If that doesn't work export the zip on your desktop top and rezip and try to reupload.
If you have professional zip software, such as winrar, test the archive is not damaged.
If your store lets you add good theme zips then you need to contact themeforest support as shopify does not support third party themes.
If your store doesn't let you add a zip shopify itself has given you contact support
Also, double-check official Avone theme installation guidelines: