code: 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);
              }
          }
      }
docs: Send a message to all devices on one or all platforms.
  
  @param Message $message
  @param string  $platform
  
  @throws PlatformNotConfiguredException
  @throws MessageTooLongException