Running build 1809 of Windows Server 2019, the server still have activation issues, IF you did not specify the product key, during installation.
If you use the GUI, it will fail, no matter what, stating that it cannot reach the company licensing activation server (KMS), but hey, I did not ever specify a KMS key, I have a MAK 😉
The solution is to use the old SLMGR.VBS script, this works..luckily 😉
Just open a command prompt and type:
“cscript c:\windows\system32\slmgr.vbs /ipk <product-key>”