API With POST Parameters in JSON Format in PHP

Sometimes parameters are arrays. In this case, such parameters should be packed into JSON. Let's look at an example. Suppose we have the following API, expecting an array in JSON format and returning the sum of the elements of this array:

api.loc/index.php<?php
  echo array_sum(json_decode($_POST['json'], true));
?>

Let's make a request to this API:

tst.loc/index.php<?php
  $url = 'http://api.loc/index.php';
  
  $curl = curl_init();
  curl_setopt($curl, CURLOPT_URL, $url);
  curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
  curl_setopt($curl, CURLOPT_POST, 1);
  
  $arr  = [1, 2, 3, 4, 5];
  $json = json_encode($arr);
  $data = ['json' => $json];
  curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
  
  $res = curl_exec($curl);
  
  var_dump($res);
?>