When you are trying to install the theme and WordPress comes back with the message 'The link you followed has expired' or 'Are you sure you want to do this?' it means that your server PHP has a setting for upload files lower than the ZIP file size (around 8,5MB). Please note that Uncode is one of the Envato top sellers and it's strictly tested by ThemeForest, this means the problem is not caused by the product (that is still not active) but by the server that prohibits the upload.

What you need to do is contact your hosting provider or follow this link to increase the ‘upload_max_filesize’ and ‘post_max_size’ to at least 32mb.