Please help me why the theme cannot be installed? I have done all the suggested methods but still declare the file is corrupt
can you tell us your purchase theme name ?
This is themeforest WordPress installation guide.
Composs - Elegant Blog, Magazine & News HTML Template
This is HTML template it will not install like wordpress!
If you want to use it at WordPress then you have to convert it into HTML to WP
Have to hire a WP developer who can convert it into WP but it can be expensive!
Ouch, does that mean I bought it wrong?
There is a WP version by the same author https://themeforest.net/item/composs-elegant-blog-magazine-news-theme/15344713 if you reach out to them then they may refund the HTML and help you buy the WP version
Good, thank you for your help.