code: def send_audio(self, recipient_id, audio_path, notification_type=NotificationType.regular):
          
          return self.send_attachment(recipient_id, "audio", audio_path, notification_type)
docs: Send audio to the specified recipient.
          Audio must be MP3 or WAV
          https://developers.facebook.com/docs/messenger-platform/send-api-reference/audio-attachment
          Input:
              recipient_id: recipient id to send to
              audio_path: path to audio to be sent
          Output:
              Response from API as <dict>