I just bought the 75" Play Gradient light strip, bridge and sync box and set up everything in the app. The lights on the strip remain the same color while watching tv.
These are my connections: I have a Yamaha receiver that is connected to the TV with an HDMI going into the eArc slot. Every other device such as cable box, NVidia Shield TV Pro and Apple TV are all connected to the receiver. I connected the HDMI cable from the out to TV slot on the sync box to the TV.
Am I missing something here?