Welcome to Vodafone Community
Does anyone have problems with WhatsApp and Facebook messenger video where they can’t hear you but you can hear them. Video call works fine on FaceTime so the microphone must be functioning? Thanks
I use Android @Shellbird123 but No I've had no issue with messenger however I'm not a user of WhatsApp.
Might be worth first checking in the apps preference settings and if necessary delete it from the apple device and from.your iTunes app section and then re download a fresh install.
An Apple Stores Genius Bar I'm sure would take a look for you too.
On a side note > Maybe the issue is with the contact your speaking with unless it's happening with all your contact connections no matter where you are.
Current Phone > Samsung Note 9 _512Gb > Model: SM-N960 Hybrid-Duos.
Samsung One Ui / Pie.
Samsung Gear s3 Frontier Watch.
This seems to be a common problem and has been raised on Apple Community.
This thread has a link to troubleshooting microphone problems: Mic problem with iPhone and whatsapp, messenger or Skype but ok with FaceTime