In the properties of your Audio Output Capture, what device are you using? This sounds like the likely issue.

Just to be clear, what kind of audio is not showing up in your video? The "desktop" audio (i.e the sound of anything on the computer, or your game if you run it on Windows), audio from a microphone, or something else (a console perhaps)?

@Mets1986

Hi. Well, I'm not familiar with recording stuff with capture cards from consoles, I always recorded my PC itself. However, I can maybe try to help with checking the issue on OBS itself, to see if you can fix it from OBS side, or check what the problem is.

Take a look at this OBS configuration:

For testing the audio of the console, you can add a new scene in OBS (optional), and then add a new resource of type "Audio Output Capture", and link it to the capture card by choosing the correct device. This new resource should be added to the default ones (Desktop + Mic/Aux), under the Audio Mixer tab. If OBS can capture the audio well, you will see the bars moving in the correct audio source (like the Desktop in my image). If not, then you know there is a problem and OBS can't detect the audio for some reason. If you can't find your capture card in the list of available audio devices, then that is another problem.

Maybe your problem can be fixed by just adding this audio resource, maybe not. As I said, not familiar with that.