If you can’t install theme and WordPress says just “Are you sure you want to do this?”, you should check your server configuration to make sure you meet all requirements mentioned in documentation: https://www.ait-themes.club/doc/hosting-requirements/
Focus mainly on option
post_max_size. Mentioned message usually appear if
post_max_size value isn’t the same like
Correct please settings on your server. If you do not have access to server settings, contact your hosting provider to change them and try to install theme again.