default value

2018/04/16, 2018/04/17, 2018/04/18, 2018/04/19, 2018/04/20, 2018/04/21, 2018/04/28

when I deal with it on the other side
how to convert it to array and send json to the specified http? Using curl

$data = array(
    "date" => $date
  );
  $data_string = json_encode($data);
  $ch = curl_init($api_signin);
  curl_setopt($ch, CURLOPT_POST, 1);
  curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
  curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
  curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/json"));
  $result = curl_exec($ch);
  curl_close($ch);

$date how to write this?