Hi George-
First, a couple of questions- how large is your backup? Are you transferring between two hosts, or from a development environment to a production environment?
Here are a couple things you can try to troubleshoot.
First, try pasting the download link directly into a browser tab to see if the download link is working. If that also fails, try making a new backup for transfer.
One of the most common causes of this issue is that the backup file is too large, or taking too long to transfer, and is timing out. If that’s the case, you may need to upload your backup file manually to restore it.