wav sound does not play on iPad 9.3.5 but plays on iPhone5

This is an IOS App developed with XCode 8.3.3. Built for target 9.3.

I have a func that is called to play a different beep, depending I swipe on right or left. But that's not the point.

    func playInputClick(direction forward: Bool) {
        var filePath: String?
        if forward {
            filePath = Bundle.main.path(forResource: "ButtonTap", ofType: "wav")
        } else {
            filePath = Bundle.main.path(forResource: "SecondBeep", ofType: "wav")
        }
           let fileURL = URL(fileURLWithPath: filePath!)
            var soundID:SystemSoundID = 0
            AudioServicesCreateSystemSoundID(fileURL as CFURL, &soundID)
            AudioServicesPlaySystemSound(soundID)
    }

When I download then run the App on iPhone 5C, IOS 10.2.1, works OK, the beeps are audible when swiping.

But on an iPad Mini, IOS 9.3.5, no sound at all.

I've check I get sound by testing in susyem preferences and ajusting some sounds.

What could be the reason ?