Почему не работает AJAX POST запрос на Heroku?

Не работает ajax post-запрос когда деплою на heroku. Выдает 403 ошибку. На localhost'ах работает норм. Даже когда проверяю через heroku local web (который по идее проделывает то же самое, что и при деплое, но на локалхосте), все работает.
CSRFToken передаю. Приложуха на React+Django.
Код:
settings.py

"""
Django settings for digitsClassifier project.

Generated by 'django-admin startproject' using Django 1.11.6.

For more information on this file, see
https://docs.djangoproject.com/en/1.11/topics/settings/

For the full list of settings and their values, see
https://docs.djangoproject.com/en/1.11/ref/settings/
"""

import os

# Build paths inside the project like this: os.path.join(BASE_DIR, ...)
BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))

# Quick-start development settings - unsuitable for production
# See https://docs.djangoproject.com/en/1.11/howto/deployment/checklist/

# SECURITY WARNING: keep the secret key used in production secret!
with open('secret_key.txt', 'r') as f:
    SECRET_KEY = f.read()

# SECURITY WARNING: don't run with debug turned on in production!
DEBUG = False

ALLOWED_HOSTS = [
    '127.0.0.1',
    '0.0.0.0',
    'digits-classifier.herokuapp.com'
]


# Application definition

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'classifier.apps.ClassifierConfig',
]

MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
]

ROOT_URLCONF = 'digitsClassifier.urls'

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [os.path.join(BASE_DIR, 'templates')]
        ,
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

WSGI_APPLICATION = 'digitsClassifier.wsgi.application'


# Database
# https://docs.djangoproject.com/en/1.11/ref/settings/#databases

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
    }
}


# Password validation
# https://docs.djangoproject.com/en/1.11/ref/settings/#auth-password-validators

AUTH_PASSWORD_VALIDATORS = [
    {
        'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.CommonPasswordValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator',
    },
]


# Internationalization
# https://docs.djangoproject.com/en/1.11/topics/i18n/

LANGUAGE_CODE = 'ru'

TIME_ZONE = 'UTC'

USE_I18N = True

USE_L10N = True

USE_TZ = True


# Static files (CSS, JavaScript, Images)
# https://docs.djangoproject.com/en/1.11/howto/static-files/

PROJECT_DIR = os.path.dirname(os.path.abspath(__file__))

STATIC_URL = '/static/'
STATIC_ROOT = os.path.join(PROJECT_DIR, 'static')

CSRF_COOKIE_NAME = "csrftoken"
CSRF_COOKIE_SECURE = True

urls.py

from django.conf.urls import url
from . import views

urlpatterns = [
    url(r'^', views.FrontendAppView.as_view(), name="index"),
    url(r'^image_add/$', views.FrontendAppView.as_view(), name="image_add"),
]

views.py

class FrontendAppView(View):
    @staticmethod
    def get(request):
        return render(request, 'classifier/index.html')


    @staticmethod
    def post(request):
        if request.POST:
            img = base64.b64decode(request.read())
            
            ...

            return HttpResponse(result, content_type='application/json')
        else:
            return render(request, 'classifier/index.html')

функция, которая передает данные на сервер.

sendData(data) {
    const self = this;

    const csrfToken = Cookies.get('csrftoken');
    axios.defaults.xsrfCookieName = "csrftoken";
    axios.defaults.xsrfHeaderName = "X-CSRFToken";
    axios({
      method: 'post',
      url: 'image_add/',
      data: data,
      headers: {
        "X-CSRFToken": csrfToken,
        "Content-type": 'application/x-www-form-urlencoded'
      }
    })
    .then(function (response) {
      console.log(response.data);
      self.setState({
        predict: response.data,
        display: "block"
      })
    })
    .catch(function (error) {
      console.log(error);
    });
  }