Windows 2025 HyperV install & adding serial number

We purchased a Dell server with Win 2025 datacenter version which entitles us to unlimited HyperV VMs.  The OS was preinstalled and did not come with an ISO for installing HyperV VMs.  I tried the ISO for the system from my Dell Digital locker but that version cannot be used for HyperV installations.   I downloaded the Microsoft freely available evaluation ISO and that installed fine.  Now I'm trying to add a serial number to make the VM production but the serial number on the the sticker on server does not work.  I used various commands:  slmgr /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX and dism /online /Set-Edition:datacenter /ProductKey:YOUR-KEY-HERE /AcceptEula.  What serial number do I use or what is the process to make the VM use a legit serial number??