How to configure the macOS firewall?
PhotoSync Companion is signed and comes with a trusted certificate to allow incoming connections even if the macOS Firewall is running. All you have to do to ensure that it works (if it isn't working already) is to go through the following steps:
Open the Security & Privacy settings in the macOS System Preferences and click the Firewall Options button on the Firewall tab to open the firewall options.
Make sure that the Automatically allow downloaded signed software to receive incoming connections checkbox is selected. This guarantees the full functionality of PhotoSync when the firewall is activated.