If you use Oasis as transmitter and connects to your TV, but no sound. Please check below step by step -
1. Make sure optical cable connection， OPT is selected on Oasis. 3.5MM or RCA audio cable connection, AUX is selected on Oasis.
2. Make sure you change your TV audio OUT setting to "External Speakers" (if using RCA Audio OUT and Optical OUT) or "Headset" (if using AUX/3.5mm OUT).
3. If your Oasis is connected to the TV digital optical output (and it's successfully paired/connected to your Bluetooth headphones) but there's no sound, it may because you need to set the TV's audio format to PCM. Oasis supports the PCM audio format only, it doesn't support Dolby, DTS.
Generally the setting should be under your TV's sound settings menu though the exact location may vary between different TVs - please refer to your TV's manual.
Go to Menu-> sound setting -> Digital (SPDIF) audio output->audio format-> set to PCM