php服务器上的$ _POST下没有显示有效的json对象

I am sending this json object to the server :

[
    {
        "row_id": 1,
        "status": "Anmeldung",
        "ma_name": "AA",
        "datum": "/",
        "fa1": "testname1",
        "fa2": "testname2",
        "limit": "10.000",
        "gruppe_kredit": "/",
        "omv_kdnr": "8124213",
        "sap_kdnr": "/",
        "fos": "/",
        "hga_kdnr": "/"
    },
    {
        "row_id": 3,
        "status": "Anmeldung",
        "ma_name": "AA",
        "datum": "/",
        "fa1": "ame1",
        "fa2": "name2",
        "limit": "12.000",
        "gruppe_kredit": "/",
        "omv_kdnr": "81515616",
        "sap_kdnr": "/",
        "fos": "/",
        "hga_kdnr": "/"
    },
    {
        "row_id": 2,
        "status": "Kunde",
        "ma_name": "AA",
        "datum": "/",
        "fa1": "newname1",
        "fa2": "newname2",
        "limit": "15.323",
        "gruppe_kredit": "/",
        "omv_kdnr": "81515616",
        "sap_kdnr": "/",
        "fos": "/",
        "hga_kdnr": "/"
    }
]

I am sending it with jquery AJAX as following:

var save = document.getElementById('save-table');
    save.addEventListener("click", function(e){
        e.preventDefault();
        getAllContents();
        console.log(updateObj);

        updateObj = JSON.stringify(updateObj);

        console.log(updateObj);
        $.ajax({
        url: "http://192.168.54.11/tabellen/logic/omv.php",
        type: "POST",
        data: updateObj,
        success: function(response){
            console.log("Success: ", response);
        },
        error: function(response){
            console.log("Error: ", response);
        }
    });
    });

My PHP Code only consists of this :

<?php 
echo "<pre>";
print_r(json_decode($_POST));
echo "</pre>";
die;
?>

When I log the response within my ajax call i just receive <pre></pre> back without any POST data. When I inspect the Network Tab Headers I can see the missing data in the Form Data part on the very bottom.

Any ideas?

Add to ajax contentType: "application/json; charset=utf-8"