code: protected function buildParams(SmsGatewayMessage $message, $to)
      {
          $optionalFields = array_filter([
              'expires_at' => data_get($message, 'expiresAt'),
              'send_at'    => data_get($message, 'sendAt'),
          ]);
  
          return array_merge([
              'number'     => $to,
              'message'    => trim($message->content),
          ], $optionalFields);
      }
docs: Build up params.
  
  @param SmsGatewayMessage $message
  @param string            $to
  
  @return array