What is the Secondary and Primary is irrelevant for sound; it is only about the sender and receiver.
Try each of the following in order.
-First, try rebooting the sender and receiver.
-Make sure you have audio enabled on both the sender and receiver:
-Make sure the Multiplicity Inbound rule is set as so on each PC:
-Try entering in the actual IP of the receiver on the sender instead of the host name and SAVE the changes:
-Disable jack detection on the sender:
-Allow the sender to be unmuted to make sure that it is indeed sending audio:
Some devices will not play sound unless output devices are indeed attached (power saving). If no speakers are on the sender, plug in some earbuds to ensure it is playing and that is indeed the issue.
-Disable any an all Firewalls (including any antivirus software) on each machine.