Q&A forums are currently English language only.
You didn't say what channel the product key was or how you tried but try as a work around, using a kms key as intermediary step.
Dism /online /Set-Edition:ServerDataCenter /ProductKey:WX4NM-KYWYW-QJJR4-XV3QB-6VM33 /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 upvote
and Accept as answer
if the reply is helpful--