Eurydace

Hi! I picked up a new LG SP9YA soundbar to go with my LG C1. It's set up via HDMI Arc. I wish to plug my Roku into the soundbar's HDMI in port and then display that to the TV. However, this does not appear to actually work. My TV simply says there is no signal. HDMI arc does work (I'm getting sound through the speakers). I also tried using a different HDMI cable connected to my laptop and that did not work either. Does anyone have any thoughts on what I'm doing wrong? Unfortunately the sound bar doesn't come with a manual specific to the Soundbar and it's literally just one page for hooking it up. Any help is appreciated!