My audio isn’t working how can I fix it

Start here:

If the microphones on your iPad aren't working - Apple Support

If you are unable to resolve the problem, you would be best advised visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad::

Genius Bar Reservation and Apple Support Options - Apple

Since we (at least, I) often overlook the obvious (and I'm not sure what app you're recording in):

1) If you are using an external mic, did you unplug the mic when you played the audio back to see if it recorded.

2) Is your playback volume turned up?