Getting error while installing Exchange on new server in Existing Exchange environment

I am installing Exchange 2016 CU8 in exisiting Exchange environment ( Existing Exchange servers  running with Exchange 2016 CU1). However, I am getting below error at first step of Exchange installation. Can any one please guide.

Error:
The following error was generated when "$error.Clear();
          $arbMbxname = [Microsoft.Exchange.Management.RecipientTasks.EnableMailbox]::DiscoveryMailboxUniqueName;
          $arbMbxLastName = "MsExchDiscoveryMailbox D919BA05-46A6-415f-80AD-7E09334BB852";
          $arbUser = @(Get-User -Filter {LastName -eq $arbMbxLastName} -IgnoreDefaultScope -ResultSize 1);
       
          if ($arbUser.Length -eq 0)
          {
            Install-UserAccount -Name $arbMbxname -LastName $arbMbxLastName;
          }
        " was run: "Microsoft.Exchange.Data.Directory.ADConstraintViolationException: An Active Directory Constraint Violation error occurred on DC03.domain.net. Additional information: The operation failed because UPN value provided for addition/modification is not unique forest-wide.
Active directory response: 000021C8: AtrErr: DSID-03200BF3, #1:
      0: 000021C8: DSID-03200BF3, problem 1005 (CONSTRAINT_ATT_TYPE), data 0, Att 90290 (userPrincipalName)
 ---> System.DirectoryServices.Protocols.DirectoryOperationException: A value in the request is invalid.
   at System.DirectoryServices.Protocols.LdapConnection.ConstructResponse(Int32 messageId, LdapOperation operation, ResultAll resultType, TimeSpan requestTimeOut, Boolean exceptionOnTimeOut)
   at System.DirectoryServices.Protocols.LdapConnection.SendRequest(DirectoryRequest request, TimeSpan requestTimeout)
   at Microsoft.Exchange.Data.Directory.GuardedDirectoryExecution.Execute[T](String bucketName, Func`1 action, Int64& concurrency)
   at Microsoft.Exchange.Data.Directory.PooledLdapConnection.GuardedSendRequest(String forestName, GuardedDirectoryExecution guardedDirectoryExecution, DirectoryRequest request, TimeSpan timeout, Func`3 sendRequestDelegate, Int64& concurrency)
   at Microsoft.Exchange.Data.Directory.PooledLdapConnection.SendRequest(DirectoryRequest request, LdapOperation ldapOperation, Nullable`1 clientSideSearchTimeout, IADLogContext logContext, Boolean shouldLogLastFilter)
   at Microsoft.Exchange.Data.Directory.ADDataSession.ExecuteModificationRequest(ADObject entry, DirectoryRequest request, ADObjectId originalId, Boolean emptyObjectSessionOnException, Boolean isSync)