Hello, I want my mr400 automaticly switch in 4G connection when i loose my adsl connection. I choose the wireless router connection and 3G/4G backup but it's not working. When i disconnect my internet

This is how my setup is: I have a local broadband for which they provided a modem Syrotech model I connected the modem to TP Link router Archer C1200 v2.0 Firmware version: 2.0.2 Build 20180118 rel.38