Re: Fortigate Migration - Vdoms & Vdoms Links
You really can't make a backup from a different version fortios and just import it in. It has to deal with the 1st 2-3 lines of the backup and many items within the fortios major version might change
If your config is not complex and the new fortigate is the same model, just copy out the interface, address, custom-services, vpn-settings, gobal settings, etc....... and paste it in to the new cfg and look things over.
In your case you might want to go back and extract the vdom settings to include policies and extract that information and add it to the new fortios version.