There is a field called “access code” in the Viking IP programming application (on the “phone numbers/phone codes” tab).  If there is a number in the access code field and you call the IP phone, you must dial this access code before you can dial the command to open the door, as extra security on inbound calls.  The access code can be disabled if this security is not required.  Remove the number from the access code field and apply the change.  You are then able to dial the relay command right away when you call the IP phone.