Why does WordPress say "The link you followed has expired" when I upload a theme?

That message during a theme upload is usually about the server rejecting the upload request, not your WordPress login expiring. First make sure you’re uploading the actual installable theme ZIP from the seller, not the whole download bundle with docs and licenses inside it. Then compare its size with the upload limit shown in WordPress. On the server, `post_max_size` has to be at least as large as `upload_max_filesize`, and both need to accommodate the theme. If you’re on managed or shared hosting, ask the host to raise the effective PHP upload/request limits; a change in one config file may not be the one WordPress is actually using.