Конвертирование base64 строки в массив байт

На страничке необходимо загрузить в input type file, а так же вывести эту картинку в img. А далее ajax запросом передать base64 строку на сервер и там перевести её в массив байт. Вот мой код View:

$('#modalWindow').on('click', '#send', function () {
        $.ajax({
            type: "POST",
            url: "/Home/LoadImage",
            data: {
                "base64img": $('#autoPicture').attr('src')
            },
            success: function (data) {
                alert('Привет');
            },
            error: function (error) {
                alert(error.responseText);
            }
        });
    });
    $('#modalWindow').on('change', '#fileLoader', function () {
        ReadImageUrl(this);
    });
    function ReadImageUrl(input) {
        if (input.files && input.files[0]) {
            var reader = new FileReader();
            reader.readAsDataURL(input.files[0]);
            reader.onload = function (e) {
                $('#autoPicture').attr('src', e.target.result);
            }
        }
    }

Код контроллера:

[HttpPost]
        public ActionResult LoadImage(string base64img)
        {
            byte[] picture = Convert.FromBase64String(base64img);
            return View();
        }

Но при попытке конвертации вылетает ошибка с текстом:

Входные данные не являются действительной строкой Base-64, поскольку содержат символ в кодировке, отличной от Base 64, больше двух символов заполнения или недопустимый символ среди символов заполнения

Хотя если использовать сайт для перевода base64 в image https://codebeautify.org/base64-to-image-converter конвертирует нормально.

Если нужен будет пример base64 кода напишите я приведу. Просто он очень большой. Могу привести например начало и конец кода, по моему по ним определяется подходит он или нет. Ну вообщем если нужен будет пример, приведу. Не понимаю почему c# не конвертирует.

Очищенная строка:

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