1) Whether the two units are connected properly, indicated by both LED lights flashes BLUE for about 2-3 seconds, and voice prompt from connected headphones / speaker “Connected”. If not, please turn both off and on again, wait for a few seconds until LED flashes correctly and you can hear the voice prompt.
If still not, then you need to manually pair them again. (Or you can refer to support.avantree.com for video instruction)
2) Check whether the audio input to the TX is valid or not > You can easily test this with a wired headphone and see whether you can hear the sound.
3) Neither of above works, please contact firstname.lastname@example.org.