Please check these articles (confirm your KMShost is correctly registered in your DNS)
https://learn.microsoft.com/en-us/deployoffice/vlactivation/configure-dns-to-activate-office-by-using-kms
Configuring DNS
Also, at the KMSclient computer, check that the KMSclient computer can discover your KMShost correctly:
nslookup _vlmcs._tcp -type=srv
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