Hi and welcome,
Cubase AI 6 was the last one officially supported macOS 10.7.
If you have activated the license already, go through the Reactivation process, please. Make sure you are entering an Activation Code to the eLCC application (the code always starts with 0240) not Download Access Code, please.
You can activate your license (what ever version it is) and then you can start older Cubase version with this license.
The problem might be, if you system doesn’t support the eLCC version, which already knows the license. For example if you would activate Cubase 10.5 license, you need the current eLCC version. An older version would find the Activation Code invalid, because Cubase 10.5 license didn’t exist prior the eLCC release.