1. Please make sure that you installed Keyboard Extension for Windows and Keyboard Extension for Android and both apps are currently running.
2. There are three connection methods available for your convenience: WiFi, Web-server, Bluetooth. Try the one which works best for you.
For vast majority of users we recommend using WiFi connection but your computer must be located within the same local network as your phone (your phone connected to the same router as your computer). Nonetheless, there is a chance that Windows firewall (or antivirus software) blocks any outgoing traffic from your computer. If that is the case you need to add keyboardextension.exe into exclusions in the firewall/antivirus software or open the ports.
If WiFi is not a working option for you, try connecting via the Web server. Normally you would not need to change firewall/antivirus software settings for that. You would need a reliable Internet connection for such a communication method.
If WiFi nor Web server are suitable for your case then try using Bluetooth connection method. Though it is a reliable one, you might notice a degrade in performance.
If none of the three communication methods work for you, please let us know. For sure we will find a solution for you.