Your config file looks fine, the mapping between Accessory0 and output5 works here.
Be sure you connected correctly the recovery buzzer to the output 5, close to the Esc outputs.
Double check if the Accessory0 slider is alive in Input tab while you move the switch in your radio.
If you changed your radio profile you may need to update the ch5/switch function.
Redo the transmitter wizard maybe ?
As reported in wiki page, if voltage is too high from the Esc/Ubec the buzzer stop working.