More docs and payments

src/pretix/api/serializers/item.py

@@ -134,6 +134,17 @@ class ItemSerializer(I18nAwareModelSerializer):
         Item.clean_per_order(data.get('min_per_order'), data.get('max_per_order'))
         Item.clean_available(data.get('available_from'), data.get('available_until'))
 
+        if data.get('issue_giftcard'):
+            if data.get('tax_rule') and data.get('tax_rule').rate > 0:
+                raise ValidationError(
+                    _("Gift card products should not be associated with non-zero tax rates since sales tax will be "
+                      "applied when the gift card is redeemed.")
+                )
+            if data.get('admission'):
+                raise ValidationError(_(
+                    "Gift card products should not be admission products at the same time."
+                ))
+
         return data
 
     def validate_category(self, value):

src/pretix/control/forms/item.py

@@ -429,6 +429,13 @@ class ItemUpdateForm(I18nModelForm):
                     'tax_rule',
                     _("Gift card products should not be associated with non-zero tax rates since sales tax will be applied when the gift card is redeemed.")
                 )
+            if d['admission']:
+                self.add_error(
+                    'admission',
+                    _(
+                        "Gift card products should not be admission products at the same time."
+                    )
+                )
         return d
 
     class Meta: