Redirection in Class Based Views Doesn't Completly Work

Question

views.py:

class LoveLetterCreateView(LoginRequiredMixin, CreateView):
    model = LoveLetter
    fields = '__all__'
    success_url = reverse_lazy('login') # NOT WORKING

class SignUpView(CreateView):
    form_class = UserCreationForm
    success_url = reverse_lazy('login') # WORKING
    template_name = 'love_letters/signup.html'

Why it would work in one CreateView but not in the other?

I tried: def get_success_url(self): - NOT WORKING.