Implement handling callbacks

app/settings.py

@@ -129,4 +129,10 @@ LOGIN_REDIRECT_URL = "/"
 # ALLOWED_PAYMENT_METHODS = ["bacs_debit", "card"]
 ALLOWED_PAYMENT_METHODS = ["card"]
 
+REST_FRAMEWORK = {
+    "DEFAULT_PARSER_CLASSES": [
+        "rest_framework.parsers.JSONParser",
+    ]
+}
+
 from app.local_settings import *  # noqa

app/urls.py

@@ -20,10 +20,11 @@ from django.urls import include, path
 from django.views.generic import TemplateView
 
 from core.ui.views.drilldown import Drilldown
-from core.views import Billing, Home, Order, Portal, Signup
+from core.views import Billing, Callback, Home, Order, Portal, Signup
 
 urlpatterns = [
     path("", Home.as_view(), name="home"),
+    path("callback", Callback.as_view(), name="callback"),
     path("billing/", Billing.as_view(), name="billing"),
     path("order/<str:product_id>/", Order.as_view(), name="order"),
     path(