First check you headphones are charged and turning on.
Are your headphones connect to the device you are trying to play music from?
If not un-pair the headphones from the device they are connected to, you can follow this guide to connect them to your new chosen device.
Check you have the "Bluetooth" volume turned up on your device, or that the app or website you are viewing is not muted.
Try using the 3.5mm audio cable provided with the headphones, this will confirm the speakers in each side are working correctly.
If the speakers are not working please contact our support team using this link.