This usually happens when the the audio device after you add a new source. Go into Settings → Audio and double-check your mic input, then look at the Audio Mixer to see if it’s muted or not showing levels. If it’s gone, just add it back as an Audio Input Capture. Restarting OBS after selecting the right mic often fixes it.
Also, since you’re getting ready for a pay-per-view live, you might want to check out platforms like VPlayed it integrates with OBS pretty smoothly and gives you built-in tools for PPV monetization, so you don’t have to worry about the setup every time.