payment.html

<form method="post">
  {% csrf_token %}
  {% if confirm %}
    <div hidden>
      {{ form.as_p }}
    </div>
    pls confirm
    <input type=submit value="Confirm" name="confirm">
  {% else %}
    {{ form.as_p }}
    <input type=submit>
  {% endif %}
</form>

views.py

from django import forms
from django.http import HttpResponse
from django.views.generic import FormView

from django.shortcuts import render


class PaymentForm(forms.Form):
    cc_number = forms.CharField()


class PaymentView(FormView):
    template_name = 'payment.html'
    form_class = PaymentForm

    def form_valid(self, form):
        if self.request.POST.get('confirm'):
            # form.save()
            return HttpResponse('done %s' % form.cleaned_data)
        else:
            return self.render_to_response({
                'form': form,
                'confirm': True,
            })


payment = PaymentView.as_view()

def payment_(request):
    if request.method == "POST":
        form = PaymentForm(request.POST)
        if form.is_valid():
            if request.POST.get('confirm'):
                # form.save()
                return HttpResponse('done %s' % form.cleaned_data)
            else:
                return render(request, 'payment.html', {
                    'form': form,
                    'confirm': True,
                })
    else:
        form = PaymentForm()
    return render(request, 'payment.html', {
        'form': form,
    })