Facebook Messenger does not provide a direct "Download" button for voice messages within its standard interface. However, you can still save these audio files by using a few simple workarounds on both desktop and mobile devices.
This is the most reliable way to extract the original audio file directly from Messenger's servers. How do I download a Facebook messenger audio file? download sound from facebook messenger
Other way is to right click on the audio file and you should get a menu list and an option within it that states ' Save audio as'. Apple Support Community Facebook Messenger does not provide a direct "Download"