[Fixed]-What more do I need to do to have Django's @login_required decorator work?

Set the LOGIN_URL in your settings. The default value is '/accounts/login/'

The decorator also takes an optional login_url argument:

@login_required(login_url='/accounts/login/')

And, from the docs:

Note that if you don’t specify the login_url parameter, you’ll need to
ensure that the settings.LOGIN_URL and your login view are properly
associated. For example, using the defaults, add the following line to
your URLconf:

(r'^accounts/login/$', 'django.contrib.auth.views.login'),

What worked for me in Django 2.2.1 – include re_path('^accounts/', admin.site.urls), in my project urls.py:

urls.py

from django.conf import settings
from django.conf.urls import include
from django.conf.urls import re_path
from django.conf.urls.static import static
from django.contrib import admin
from django.urls import path

urlpatterns = [
    path('admin/', admin.site.urls),
    re_path('^accounts/', admin.site.urls),
]

And in my views.py:

views.py

from django.contrib.auth.decorators import login_required
from django.views.generic import TemplateView

@method_decorator(login_required, name='dispatch')
class HomePageView(TemplateView):
    """
    Home Page View
    """
    template_name = 'amp/home.html'

Hope that helps.

UPDATE: To avoid warnings from django in regards to admin urls being loaded twice, I used a redirect instead in urls.py:

urls.py

urlpatterns = [
    re_path('^accounts/', admin.site.urls),
    re_path(r'^admin/', RedirectView.as_view(url='/accounts/', permanent=True))
]

More on redirect view here.

path('accounts/login/', admin.site.urls),

Add this line in your urls.py project folder. Then it will work fine.

from django.contrib.auth.decorators import login_required
@login_required(login_url='/accounts/login/')

Add above two lines in your views.py file.