Please make sure that you have enabled the proper settings on your TV to use ARC. If you have a TCL Roku TV, you can visit https://support.tclusa.com/23507-roku-tv/connecting-a-sound-bar-to-your-tv-using-arc for more information. Hope this helps! Thank you, TCL Customer Support
The HDMI ARC has to be enabled. You need to get to the right place in settings to do this. I went to the TCL web page and browsed around until I found a question and answer explaining how to enable the setting. It also turns out that my television's HDMI ARC also had to be enable in settings.