buzz out all adjacent pins and then do a continuity test on all pins.
Interface to the board removed from a generic BT audio receiver.
NOTE that the numbering on the .5mm side of the breakout board is inverted, ie 1=24 ...24=1 as connector is actually mounted upside down.
Bridge pins 1,2,3 (22,23,24 as labelled on breakout board.), on breakout board and connect to audio ground on receiver board.
Bridge pins 4,5 (20,21 as labelled on breakout board.)and then connect to USB 5v on receiver board . Also bridge between pins 14 and 15 (11 to 10 on breakout board) to the 5v pins in previous step for "bt_det" pull up.
Connect pins 6 and 7 (18,19 as labelled on breakout board.)to respective audio channels.
Connect pin 12 (13 on breakout board) to USB 0v on receiver board.
are you willing to sell one of these?