The headphones are fully charged so I know that isn't an issue. I've tried restarting my iPhone 6s and the headphones to connect them again. All the functions work, like turning up the volume and changing a song, I just can't hear anything from the headphones. My Bluetooth icon at the top part of my iPhone won't show up gray (showing that something is connected) or show the battery. I have had my phone connected to other Bluetooth devices like speakers and it works fine.
Read more: IWorld headphones are connected to my iPhone but I can't hear sound?