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.