Roqos cellular backup connection is initiated when the Ethernet based connection to your main ISP (DSL/Cable/Satellite) goes down, your ISP modem breaks, or your ISP has a backbone problem.
Your Roqos cellular router restores your ISP connection when the problem on the ISP connection is fixed.
You can simply test cellular connection by disconnecting the Ethernet cable connected to your ISP modem/router, and wait for a minute. When it is established the Roqos app's home page will show Cellular Connection Active. In addition RC20 model's Roqos logo will illuminate green during cellular connection.
For cellular connection to work, you also need to have active Roqos cellular service which you can purchase at Roqos Customer Portal https://www.roqos.com/customer-portal/login
You can check your cellular and Ethernet based Internet usage on your Roqos app in Settings > Data Usage page: