Don't worry! This is a common issue raised with many apps like ours that have been programmed to respect your device's mute button. Many apps ignore your mute switch so that's why you may still be able to hear the sound from some of your apps.
It's quick & easy to solve. First, check that the side switch on your device is not set to mute. Then, double check your side-switch settings in your control center. You may find that your side-switch has been set to use as a 'rotation-lock' switch. You will need to change it back to work as a 'mute switch' before you can un-mute your device.
Do get in touch with us if you need any further help as the sound settings on devices can be confusing.