Submit Task Status Update through the REST API (2013)

How can I submit an update to tasks's status through the REST API?

Tried POSTing to the StatusTask endpoint with no luck -- received a 403 error. I think I'm going about it completely wrong, but here's what I was trying so far (as a test):

function updateStatus() {
    $.ajax({
        url: url + "/_api/ProjectServer/EnterpriseResources('c4b3a7c4-6cdc-e311-8c25-0022198e7bfe')/Assignments('62bbf75b-6600-e411-8f19-c2a93d88a488')/Task/",
        dataType: "json",
        type: "POST",
        contentType: "application/json",
        data: JSON.stringify({"__metadata": {type: "PS.StatusTask"},
            percentComplete: 0.10
        }),
        beforeSend: function (xhr) {
            xhr.setRequestHeader("ACCEPT", "application/json; odata=verbose");
        },
        headers: {"Content-Type": "application/json;odata=verbose","X-RequestDigest": $("#__REQUESTDIGEST").val(),"IF-MATCH": "*","X-Http-Method": "PATCH"
        },
        success: successFunc,
        error: errorFunc,
    });
}