Here is a solution that may help, please try the following steps:

1. Go to your phone Bluetooth Menu and click the Forget the Bluetooth device (headphone or car stereo)

2. Turn OFF the Bluetooth device

3. Turn the phone Bluetooth Off

4. Restart your phone

5. Open Castbox app

6. Turn ON the Bluetooth device

7. Turn your phone's Bluetooth ON and pair the Bluetooth device.