fix test

src/pretix/api/serializers/media.py

@@ -160,7 +160,7 @@ class ReusableMediaSerializer(I18nAwareModelSerializer):
                     ops_noperm.append(lop.id)
             if ops_noperm:
                 ops = [
-                    {'id': op.id} if op.id in ops_noperm 
+                    {'id': op['id']} if op['id'] in ops_noperm 
                     else op
                     for op in ops
                 ]

src/tests/api/test_reusable_media.py

@@ -276,7 +276,7 @@ def test_medium_detail_event_permission_missing(token_client, organizer, event,
         ticket = event.items.create(name='Early-bird ticket', category=None, default_price=23, admission=True,
                                     personalized=True)
         op = o.positions.create(item=ticket, price=Decimal("14"))
-        medium.linked_orderposition = op
+        medium.linked_orderpositions.add(op)
         medium.linked_giftcard = giftcard
         medium.customer = customer
         medium.save()