Finally got an input form. :-)

lostplaces/lostplaces_app/templates/voucher-verify.html

@@ -8,8 +8,8 @@
 <h2>Voucher-Überprüfung</h2>
 <form method="post">
   {% csrf_token %}
-  {{ form.as_p }}
-  <button type="submit">Login</button>
+  {{ voucher_form.as_p }}
+  <button type="submit">Überprüfen</button>
 </form>
 
 {% endblock maincontent %}

lostplaces/lostplaces_app/views.py

@@ -21,7 +21,8 @@ class VoucherVerify(View):
     fields = ['code']
     
     def get(self, request, *args, **kwargs):
-        return render(request, 'voucher-verify.html')
+        voucher_form = VoucherVerifyForm()
+        return render(request, 'voucher-verify.html', {'voucher_form': voucher_form})
 
 class SignUpView(CreateView):
     form_class = ExplorerCreationForm