Make sure the domain exists on the primary name server, backup primary name server, and 2nd backup primary name servers prior to creating secondary domain.
In addition you need to have whitelisted our AXFR IP's for the zone addition to be successful.
For more information on how to whitelist our name servers see What IPs need to be whitelisted for zone transfer and NOTIFY to Neustar?
1. Log into portal.ultradns.com
2. Click on Domains tab
3. Click on + Add Domain button
4. Enter Domain Name:
5. Click on Secondary Domain
6. Enter Primary Name Server: (Required)
7. Check Use TSIG Key checkbox
8. Check Auto-generate Key checkbox
9. Enter 1st Backup Primary NS: (Optional)
10. Check Use TSIG Key checkbox (Optional)
11. Enter 2nd Backup Primary NS: (Optional)
12. Check Use TSIG Key checkbox (Optional)
13. Enter Notification Email: (Optional)
14. Enter Change Comment: (Optional)
15. Click Save button
Please note the ? icons throughout the portal and click them for more details: