使用contentType调用Ajax：'application / json'

When I remove the content-Type it works, but jsonitem received in php side has syntax errors I found in other posts that I should definitely precise the content type when sending Json objects.

this code returns "failed func"

var json = {
  test: "testv"
};

var data = {
  action: 'ajax_load_article',
  jsonitem: JSON.stringify(json),
};

var options = {
  url: beloadmore.url,
  dataType: "json",
  contentType: "application/json;charset=utf-8",
  type: "POST",
  data: data,
  success: function(res, status, xhr) {
    if (res.success) {
      console.log(res);
      $('.site').append(res.data);
    } else {
      console.log("failed func");
      console.log(res);
    }
  },
  error: function(xhr, status, error) {
    console.log(xhr.responseText);
    console.log(error);
  }
};
$.ajax(options);

EDIT:

php file:

$jsonitem= $_POST['jsonitem'];
$jsonitemdecoded = json_decode($jsonitem);

echo "jsonitem".$jsonitem;
echo "jsonitemencoded".$jsonitemdecoded;
echo json_last_error_msg();

echo screens when I remove contentType: 'application/json' :

jsonitem {\"test\":\"testv\"}

jsonitemencoded Syntax error

If you use application/json as content type for the request, you should serialize the object to json before post it;

JSON.stringify(data);