Getting an error 405 when submitting formview from detailview

I have the detailview, formview, and mail working. But it gives me a 405 error instead of redirecting back to the page. Please give me some eyes. I cannot see why it is not working. I have recently 3 switched # from .net mvc to python/django. Thank you for any help.

FORMS.PY

class MessageSellerForm(forms.Form):
contact_name = forms.CharField(max_length=100, required=True)
contact_email = forms.EmailField(required=True)
content = forms.CharField(required=True, widget=forms.Textarea)

VIEWS.PY class PostDetailView(DetailView): model = Ad template_name = 'x_ads/ad_detail.html'

def get_context_data(self, **kwargs):
    context = super(PostDetailView, self).get_context_data(**kwargs)
    context['form'] = MessageSellerForm
    return context




    class PostDetail(View):

    def get(self, request, *args, **kwargs):
      view = PostDetailView.as_view()
      return view(request, *args, **kwargs)

def post(self, request, *args, **kwargs):
    view = PostDetailView.as_view()
    return view(request, *args, **kwargs)


class PostMessageSeller(SingleObjectMixin, FormView):
template_name = 'x_ads/ad_detail.html'
form_class = MessageSellerForm
success_url = '/'

subject = 'User message about your ad'
from_email = '********'
to_email = '*********'
message = '**********'
send_mail(subject=subject, message=message, from_email=from_email,
          recipient_list=[to_email], fail_silently=False)

model = Ad

def post(self, request, *args, **kwargs):
    if not request.user.is_authenticated:
        return HttpResponseForbidden()
    self.object = self.get_object()
    return super().post(request, *args, **kwargs)

ad_detail.html

<form method="POST">
        {% csrf_token %}
        <fieldset class="form-group">
            {{ form|crispy }}
        </fieldset>
        <div class="form-group">
            <button class="btn btn-1 btn-sm" type="submit">Message Seller</button>
        </div>
    </form>

It display the detail model, so I add a Comment section in the DetailView page using ModelFormMixin.

This is my .py code

def get_context_data(self, *args, **kwargs):
    context = super(PostDetailView, self).get_context_data(*args, **kwargs)
    context['form'] = self.get_form()
    return context

def get_absolute_url(self):
    return reverse(request, 'basic_app:post_detail', kwargs={'pk':self.pk})