Simple!
 

1. Turn on your device and open DISPL Player, to make it "Online". 
   
2. Use the Web Browser (like Internet App, on Linux) to test if your device can access any common website such as "www.google.com". If not possible, then stop this guide, for you truly have an internet access issue. Check router and your internet provider. If it was possible, follow the next steps.
    
3. On your computer, open your CMS platform > Devices. Check if the status of your device is "Offline". This may indicate you have a firewall. If status is "Online", "Pause" or "Playback", device is OK.  
   
4.  At the device running DISPL Player, close DISPL Player, return to the web browser, and go to http://api.displayforce.ai . If the website doesn't open, and shows as "Page not found", firewall issue is confirmed. It should appear as below.
   

5. Follow the whitelist guide, to allow DISPL servers to be accessed through your device.
    

   Done!