def send_audio(self, recipient_id, audio_path, notification_type=NotificationType.regular):
        """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>
        """
        return self.send_attachment(recipient_id, "audio", audio_path, notification_type)