src/Message.php
public function audio($resource, $isReusable = false)
    {
        $payload = [
            'is_reusable' => $isReusable
        ];

        if (is_int($resource)) {
            $payload['attachment_id'] = $resource;
        } else {
            $payload['url'] = $resource;
        }

        $this->setAttachment('audio', $payload);

        return $this;
    }
public function audio($resource, $isReusable = false)
    {
        $payload = [
            'is_reusable' => $isReusable
        ];

        if (is_int($resource)) {
            $payload['attachment_id'] = $resource;
        } else {
            $payload['url'] = $resource;
        }

        $this->setAttachment('audio', $payload);

        return $this;
    }
Populate audio

@param string|int $resource Url or attachment id
@param bool $isReusable Is reusable

@return Message