When we have seen type of issue in the past it was most often due to a firewall blocking Roon somewhere along the line. Can you please use these instructions (<-Clickable link) to make sure that you have added both Roon and RAATServer as exceptions to your OSX firewall?
If you have any active antivirus or firewall applications installed on that PC (such as Bullguard/Little Snitch/McAFee/ect.) is there any change in behavior if you temporarily disable this? If there is a change when this firewall is disabled, then we know to take a closer look and add an exception for Roon to it.
I would also make sure that the zones have been enabled in Roon Settings -> Audio before attempting to play back audio to it. You can find out more info about Roon zones in this guide and once you have enabled the zone, you can switch to it by using the zone picker.
Note: iPhone/iPad zones by default are “Private Zones” and if you want to control these zones from your Macbook, you will need to ensure that you have disabled the Private Zones Toggle in the Device Setup Tab: