What channel is the product key? (OEM, retail, volume) Might try as a workaround using a kms key as intermediary step.
Dism /online /Set-Edition:ServerStandard /ProductKey:VDYBN-27WPP-V4HQT-9VMD4-VMK7H /AcceptEula
then if successful use your own product key below after reboot
slmgr /ipk xxxxx-xxxxx-xxxxx-xxxxx-xxxxx
slmgr /ato
--please don't forget to Accept as answer if the reply is helpful--