$.ajax({
            type: "GET",
            crossOrigin: true,
            url: "http://www.nexdomain.com/test.php?callback=?",
            dataType: "jsonp",
            data: {"test":"123"},
            cache: false,
            scriptCharset: "utf-8",
            contentType: "application/x-www-form-urlencoded; charset=UTF-8",
            success: function(data) {
                console.log(data);
                omw_sql(data);
            },
            error: function (jqXHR, textStatus, errorThrown) {
                alert(jqXHR.responseText); // тут пусто
            }
        });

function errHND($errno, $errstr, $errfile, $errline)
{
    http_response_code(200); // не помогло
    echo $errstr;
    return true;
}