Probably worth contacting support.
Click the little blue button to get the file needed. Save it on a portable drive and carry it to a computer with internet access. Upload that file to the IA servers via IA website’s activation tool. You will get a license file from that to put back on the portable drive. Carry that back to the isolated location and upload using the file chooser button.
If you’ve followed the process outlined by @pturmel, have uploaded the (recently obtained, never used before) activation file received by IA, and are still getting that Unable to process activation request error, then…