Sometimes it says there is an error or a duplicate error but actually, the demo has already been uploaded. To check this, just go to your Pages > All pages > if you see pages there then you have successfully imported the demo content and if you also go to your Menus > main nav you will notice that there are several duplicates that were created reflecting how many times you uploaded the demo content.
If you are not seeing any Pages, content & menus that means your PHP limits need adjustment.
An expired error usually happens if your PHP limits cannot handle the theme upload.
The PHP levels you need to increase specifically are:
upload_max-Size = 64m or higher
post_maxsize = 96m or higher
PHP version 7.0 or higher
You can do this in the cPanel of some hosts or by simply contacting your host and asking them to do this for you.