public function broadcast(Message $message, ?string $platform = null)
    {
        if (null !== $platform && !isset($this->arns[$platform])) {
            throw new PlatformNotConfiguredException("There is no configured ARN for $platform");
        }

        if ($platform) {
            $this->broadcastToPlatform($message, $platform);
        } else {
            foreach ($this->arns as $platform => $arn) {
                $this->broadcastToPlatform($message, $platform);
            }
        }
    }