In case your Sync box and TV backlight is not working properly, check if:

• Your have the WiZ V2 app version from 1.25.6 or above. Note: if you have paired/set up the Sync box in an older app version, you'll need to delete it and pair it again in the new app version.
• An "external" HDMI device (e.g. streaming stick or gaming console) is plugged into the Sync box's 'HDMI IN' port.
• You have the display setting no higher than 4K @60Hz and have turned off VRR, ALLM functions as well as other gaming mode or low latency mode in both gaming console and TV. 
• (In case you have multiple sync boxes in the Home) You haved selected the right sync box. If not, you can tap below the "sync box icon" in the Video sync page to switch to another sync box.