In order to bring in audio from your mixer, you must convert your audio signal to a TRRS (Tip-Ring-Ring-Sleeve) signal. This will allow an iOS device to receive the audio input from your mixer. Below are a few options you can use to convert your audio signal.
Note: If you have an iPhone 7/8/X or 7/8 Plus you will also need to use the Lightning to 3.5mm Headphone Jack adapter that was included with your iPhone.
We also have this awesome video explaining how to connect your board audio into your iPad / iPhone.