public function sendFile(Channel $channel, $filepath, $filename, $content, $tts)
    {
        $multipart = [
            [
                'name'     => 'file',
                'contents' => fopen($filepath, 'r'),
                'filename' => $filename,
            ],
            [
                'name'     => 'tts',
                'contents' => ($tts ? 'true' : 'false'),
            ],
            [
                'name'     => 'content',
                'contents' => (string) $content,
            ],
        ];

        return $this->runRequest(
            'POST',
            "channels/{$channel->id}/messages",
            null,
            [],
            false,
            false,
            ['multipart' => $multipart]
        );
    }