Recently I have migrated several servers from Vultr to Microsoft Azure.

As part of this migration, windows became un-activated – most likely because Vultr runs it’s own KMS service and it is no longer able to contact the server:

In order to resolve this, I changed the product key to Microsoft’s KMS key.

Then the KMS server was changed to Microsoft’s, and activation was forced: (run from administrative command prompt)

cscript c:\windows\system32\slmgr.vbs /ipk <product key>
cscript c:\windows\system32\slmgr.vbs /skms kms.core.windows.net:1688
cscript c:\windows\system32\slmgr.vbs /ato