Use SETSPN -L ServiceAccountName to list the Service Principals. Use SETSPN -X to check for duplicate Service Principal Names. ...

Use [SETSPN -L ServiceAccountName] to list the Service Principals.
Use [SETSPN -X] to check for duplicate Service Principal Names.

If SPN is duplicated for the AD FS service account, remove the SPN from the duplicated account using [SETSPN -d service/namehostname]

If SPN is not set, use [SETSPN -s {Desired-SPN} {domain_name}\{service_account}] to set the desired SPN for the Federation Service Account.