Apple changed the functionality of the button above the volume controls on the iPad to work as a mute button and a screen lock button. Make sure this mute button is turned off when you use the app and that should fix any sound issues. If it's still not fixed, there is a control in the settings section of your iPad that  allows for changes to its functionality.

Go to Settings - General - Make sure the mute button is checked as below:

Please feel free to contact us if you need additional help.

Thanks