By default, Splashtop Center will use Port 443. However, you can configure it to use a different port if another application is already using this port.
If Splashtop Center is blocked by Windows Firewall (from Self Diagnostic test result code 0x00030101), you may want to put Splashtop Center in the exception list in Windows Firewall. Please refer to Microsoft support link for more information on Allow a program to communicate through Windows Firewall.
https://windows.microsoft.com/en-us/windows-vista/open-a-port-in-windows-firewall