The problem is no Roku is bluetooth transmitter, which what your Bluetooth soundbar is looking for, just like Roku tv your bluetooth soundbar are receivers only, two receivers can't communicate with each other. Sorry. Roku Soundbars don't use bluetooth to communicate with Roku tv, they use WIFI-Direct, a different kind of RF signal then Bluetooth. Anyways Roku Soundbars are hardwired to Roku Tv's by hdmi-arc, or hdmi plus optical. Sound is not transmitted wirelessly.
Edmund
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee.