Failure Notice "Are you sure you want to do this?!"

Can someone please help me and tell me why when I try to upload a theme that I just bought, it won’t upload and it comes up a failure notice that says “Are you sure you want to do this?”

I’ve talked to the people that work for the company that I bought the theme for but they said there wasn’t an issue with the theme and that it was on my side of things.

I’m irritated because I’ve tried uploading on three different browsers and they won’t refund my money.

PLEASE HELP ME