My black E7 headphones won't play any sounds

Hello, after doing some searching, I've found that it may be a bluetooth connection issue. What this means is more than likely an issue with the device you're trying to connect to instead of the headphones. I would recommend checking if all your software is up to date or a simple reset should do. If the problem persists, then I would recommend following this troubleshooting guide. I hope this helps!

Cowin E7 Troubleshooting