Aporte original por: MrCatsoup ,
Try powering on yourJBL Charge 4 first and wait for the LED indicator to turn on. Then try holding down the play/pause button and the volume up button up to 20 seconds and that should factory reset your device. Then try again and see if it makes sound. I personally have a JBL Xtreme and I’ve had similar problem and factory reset fixed mine. Hopefully it works for you too.