I installed a Windows Server 2019 core evaluation (no desktop experience).
When adding the product key it fails.
DISM /Online /Set-Edition:ServerStandardCor /ProductKey:N69G4-B89J2-4G8F4-WWYCC-J464C /AcceptEula
The above step is necessary to transform the evaluation version to retail version using the Generic Volume License Keys, but it fails with error 1168
I read there is a bug for the core version and it is not possible to activate, but it sounds weird.
The problem is the same described here and at the end it seems the author filed a bug report which seems to be open, but I don't know if that platform is the official Microsoft one for tracking bugs.
So according to my experience it is not possible to activate a Windows Server 2019 core evaluation with a volume license key, you can only activate Windows Server 2019 evaluation, the one with the desktop experience.
The reason I asked here is that I spent hours reading lots of suggestions on internet, but all of them refer to the non-core version.
I think there is a lack of visibility for this bug, the official documentation reports this limitation only for the older Windows Server 2016 and it is very difficult to find.
WORKAROUND
Today I downloaded the iso for volume licence, I installed the core version and could easily activate it.