Hello,
I would start by looking at the Application Event logs and by the data output from SLMGR /DLV run in an elevated cmd prompt.
here is the article explaining the output o each of those.
https://learn.microsoft.com/en-us/windows-server/get-started/activation-troubleshoot-kms-general
I would look at the DNS server KM HOST record and make sure it is correct, it could be the name of the host being reported by the DNS server is not correct.
Also check that to see if there are multiple DNS Server records on the DNS Server
If that does not work, post the application event log and the output rom slmgr /dlv.
Darrell