The connection may fail because:
1. Your router can have a hardware firewall that is blocking all incoming and outgoing traffic for the ports that are used by SyncMate.
In this case you should open corresponding ports in your router’s firewall:
- port 27384 for syncing with Mac computers
- port 27385 for syncing with Windows PCs
Here you can find instructions on how to do it.
2. Your computers/devices are located in different subnetworks. In this case, you should configure port forwarding for the above port(s), as advised here.