Chosen Solution
Hi have got a iPhone 8 Plus, the mic works fine for phone calls, on both handset and loudspeaker, but as soon as you try making a Facebook call, video or make a audio recoding no sound gets played or picked up at all. Have tried replaceing the front camera flex as thought it was this mic but tried a couple of known working ones but no joy, have also replaced the bottom mics with the charging port with no joy
This might be a software issue, you can try reinstalling iOS on your phone, using iTunes or 3uTools. Make sure to backup your data before doing this, because doing this will wipe all of the data from your iPhone.
