I have the following code.

$(".likeBack").on("click", function(){
  var user = $(this).attr("user");
  var theLikeBack = $(this).closest(".name-area").find(".theLikeBack");
  $.ajax({
    type: "POST",
    dataType: "json",
    url: "processes/rewind-knock.php",
    data: "user="+user+"&type=likeback",
    success: function(json){
      alert("SUCCESS");
    },
    error: function(jqXHR, textStatus, errorThrown){
      alert("XHR: " + jqXHR + " | Text Status: " + textStatus + " | Error Thrown: " + errorThrown);
    }
  });
});

Here, everything is functional. Network tab shows request and response well received as required. However, the success part is not getting executed. I tried adding beforeSend and complete and both are getting executed but success part (nothing inside the success blog is getting executed). I don't understand the reason why.

UPDATE

Add error part. It returns:

XHR: [object Object] | Text Status: parsererror | Error Thrown: SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

UPDATE 2

Screenshot