Fix handling unknown payment provider

src/pretix/base/services/orders.py

@@ -678,6 +678,13 @@ def _cancel_order(order, user=None, send_mail: bool=True, api_token=None, device
 
     for p in order.payments.filter(state__in=(OrderPayment.PAYMENT_STATE_CREATED, OrderPayment.PAYMENT_STATE_PENDING)):
         try:
+            if not p.payment_provider:
+                raise PaymentException(
+                    _("The payment {payment} could not be canceled as the payment provider ({provider}) is not available anymore.").format(
+                        payment=str(p),
+                        provider=p.provider
+                    )
+                )
             with transaction.atomic():
                 p.payment_provider.cancel_payment(p)
                 order.log_action(

src/pretix/control/views/orders.py

@@ -874,6 +874,13 @@ class OrderPaymentCancel(OrderView):
     def post(self, *args, **kwargs):
         if self.payment.state in (OrderPayment.PAYMENT_STATE_CREATED, OrderPayment.PAYMENT_STATE_PENDING):
             try:
+                if not self.payment.payment_provider:
+                    raise PaymentException(
+                        _('The payment {payment} can not be canceled as the payment provider "{provider}" is not available anymore.').format(
+                            payment=str(self.payment),
+                            provider=self.payment.provider
+                        )
+                    )
                 with transaction.atomic():
                     self.payment.payment_provider.cancel_payment(self.payment)
                     self.order.log_action('pretix.event.order.payment.canceled', {
@@ -898,6 +905,16 @@ class OrderPaymentCancel(OrderView):
         return redirect(self.get_order_url())
 
     def get(self, *args, **kwargs):
+        if not self.payment.payment_provider:
+            messages.error(
+                self.request,
+                _('The payment {payment} can not be canceled as the payment provider "{provider}" is not available anymore.').format(
+                    payment=str(self.payment),
+                    provider=self.payment.provider
+                )
+            )
+            return redirect(self.get_order_url())
+
         return render(self.request, 'pretixcontrol/order/pay_cancel.html', {
             'order': self.order,
         })
@@ -1077,6 +1094,16 @@ class OrderPaymentConfirm(OrderView):
         return redirect(self.get_order_url())
 
     def get(self, *args, **kwargs):
+        if not self.payment.payment_provider:
+            messages.error(
+                self.request,
+                _('The payment {payment} can not be confirmend as the payment provider "{provider}" is not available anymore.').format(
+                    payment=str(self.payment),
+                    provider=self.payment.provider
+                )
+            )
+            return redirect(self.get_order_url())
+
         return render(self.request, 'pretixcontrol/order/pay_complete.html', {
             'form': self.mark_paid_form,
             'order': self.order,

src/pretix/presale/views/order.py

@@ -355,10 +355,11 @@ class OrderDetails(EventViewMixin, OrderDetailMixin, CartMixin, TicketPageMixin,
                 ctx['last_payment'] = lp
 
                 pp = lp.payment_provider
-                ctx['last_payment_info'] = pp.payment_pending_render(self.request, ctx['last_payment'])
+                if pp:
+                    ctx['last_payment_info'] = pp.payment_pending_render(self.request, ctx['last_payment'])
 
-                if lp.state == OrderPayment.PAYMENT_STATE_PENDING and not pp._payment_abort_pending_allowed(lp):
-                    ctx['can_pay'] = False
+                    if lp.state == OrderPayment.PAYMENT_STATE_PENDING and not pp._payment_abort_pending_allowed(lp):
+                        ctx['can_pay'] = False
 
             ctx['can_pay'] = ctx['can_pay'] and self.order._can_be_paid() is True