TC500 bluetooth transmitter doesn't work with Monoprice BT600ANC headphones

 The transmitter works with all my other BT headphones but the Monoprice pairs and connects, but no sound.  The "LL" led is lit but I do not think the headphones support that codec.  Has anyone got a suggestion.

I just looked up the Monoprice BT600ANC, they indeed do not support the LL codec. The transmitter should be showing SBC instead of LL when connected with the Monoprice. One thing you can try is to factory reset the transmitter by pressing and holding the - and + buttons together for a couple seconds.