Fixes, cleanup, rebase

src/pretix/api/serializers/checkin.py

@@ -99,6 +99,13 @@ class CheckinRPCRedeemInputSerializer(serializers.Serializer):
         super().__init__(*args, **kwargs)
         self.fields['lists'].child_relation.queryset = CheckinList.objects.filter(event__in=self.context['events']).select_related('event')
 
+    def validate(self, attrs):
+        exchange_fields = ["exchange_medium_type", "exchange_medium_identifier", "exchange_link_action"]
+        if any(attrs.get(k) is None for k in exchange_fields) and not all(attrs.get(k) is None for k in exchange_fields):
+            raise ValidationError("If you set any of exchange_medium_type, exchange_medium_identifier, or "
+                                  "exchange_link_action, you need to set all of them.")
+        return attrs
+
 
 class MiniCheckinListSerializer(I18nAwareModelSerializer):
     event = serializers.SlugRelatedField(slug_field='slug', read_only=True)

src/pretix/api/views/checkin.py

@@ -466,7 +466,7 @@ def _redeem_process(*, checkinlists, raw_barcode, answers_data, datetime, force,
 
     device = auth if isinstance(auth, Device) else None
     gate = gate or (auth.gate if isinstance(auth, Device) else None)
-    media = None
+    medium = None
 
     context = {
         'request': request,
@@ -805,15 +805,12 @@ def _redeem_process(*, checkinlists, raw_barcode, answers_data, datetime, force,
         locale = op.order.event.settings.locale
     with language(locale):
         try:
-            exchange_requested = any(k is not None for k in [exchange_medium_type, exchange_medium_identifier, exchange_link_action])
+            if exchange_link_action and medium:
-
+                # Cannot scan a medium and then request to exchange it
-            if exchange_requested:
+                raise CheckInError(
-                if any(k is None for k in [exchange_medium_type, exchange_medium_identifier, exchange_link_action]):
+                    gettext('You cannot exchange a medium for a medium.'),
-                    raise ValidationError("If you set any of exchange_medium_type, exchange_medium_identifier, or "
+                    'error'
-                                          "èxchange_link_action, you need to set all of them.")
+                )
-                if medium:
-                    # Cannot scan a medium and then request to exchange it
-                    raise ReusableMedium.DuplicateEntry()
 
             checkin_args = dict(
                 op=op,
@@ -836,7 +833,7 @@ def _redeem_process(*, checkinlists, raw_barcode, answers_data, datetime, force,
                 reusable_medium=medium,
             )
 
-            if exchange_requested:
+            if exchange_link_action:  # other fields are filled, see CheckinRPCRedeemInputSerializer.validate
                 with transaction.atomic():
                     # Do exchange and check-in atomically, i.e. both succeed or both fail
                     medium = perform_media_exchange(
@@ -848,11 +845,9 @@ def _redeem_process(*, checkinlists, raw_barcode, answers_data, datetime, force,
                         user=user,
                         auth=auth,
                     )
-                    source_type = media.media_type.identifier
+                    source_type = medium.media_type.identifier
-                    checkin_args['medium'] = medium
+                    checkin_args['reusable_medium'] = medium
-                    perform_checkin(
+                    perform_checkin(**checkin_args)
-                        reusable_media=media,
-                    )
             else:
                 perform_checkin(**checkin_args)
         except RequiredQuestionsError as e:
@@ -877,26 +872,6 @@ def _redeem_process(*, checkinlists, raw_barcode, answers_data, datetime, force,
                 'list': MiniCheckinListSerializer(list_by_event[op.order.event_id]).data,
                 'reason_explanation': e.msg,
             }, status=400)
-        except ReusableMedium.DoesNotExist:
-            return Response({
-                'status': 'error',
-                'reason': Checkin.REASON_MEDIUM_INVALID,
-                'reason_explanation': 'Reusable medium identifier not found',
-                'require_attention': op.require_checkin_attention,
-                'checkin_texts': op.checkin_texts,
-                'position': CheckinListOrderPositionSerializer(op, context=_make_context(context, op.order.event)).data,
-                'list': MiniCheckinListSerializer(list_by_event[op.order.event_id]).data,
-            }, status=400)
-        except ReusableMedium.DuplicateEntry:
-            return Response({
-                'status': 'error',
-                'reason': Checkin.REASON_MEDIUM_EXISTS,
-                'reason_explanation': 'Reusable medium identifier already exists',
-                'require_attention': op.require_checkin_attention,
-                'checkin_texts': op.checkin_texts,
-                'position': CheckinListOrderPositionSerializer(op, context=_make_context(context, op.order.event)).data,
-                'list': MiniCheckinListSerializer(list_by_event[op.order.event_id]).data,
-            }, status=400)
         except CheckInError as e:
             if not simulate:
                 op.order.log_action('pretix.event.checkin.denied', data={

src/pretix/base/models/media.py

@@ -138,9 +138,6 @@ class ReusableMedium(LoggedModel):
         ]
         ordering = "identifier", "type", "organizer"
 
-    class DuplicateEntry(Exception):
-        pass
-
 
 class MediumKeySet(models.Model):
     organizer = models.ForeignKey('Organizer', on_delete=models.CASCADE, related_name='medium_key_sets')

src/pretix/base/services/media.py

@@ -23,10 +23,13 @@ import secrets
 
 from django.db import IntegrityError
 from django.db.models import Q
+from django.utils.translation import gettext as _
 from django_scopes import scopes_disabled
 
-from pretix.base.models import GiftCardAcceptance, Item
+from pretix.base.media import MEDIA_TYPES
+from pretix.base.models import Checkin, GiftCardAcceptance, Item
 from pretix.base.models.media import MediumKeySet, ReusableMedium
+from pretix.base.services.checkin import CheckInError
 
 
 def create_nfc_mf0aes_keyset(organizer):
@@ -88,14 +91,47 @@ def perform_media_exchange(organizer, media_type, identifier, link_action, link_
     if link_action not in ('append', 'replace'):
         raise ValueError("Invalid link_action")
 
-    if media_policy == Item.MEDIA_POLICY_REUSE:
+    if media_type not in MEDIA_TYPES:  # should be caught by serializer already
-        # Will and should raise ReusableMedium.DoesNotExist if not found
+        raise CheckInError(
-        medium = ReusableMedium.objects.get(
+            _('Invalid medium type.'),
-            type=media_type,
+            Checkin.REASON_ERROR,
-            identifier=identifier,
+            reason=_('Invalid medium type.'),
-            organizer=organizer,
         )
 
+    if not MEDIA_TYPES[media_type].is_active(organizer):
+        raise CheckInError(
+            _('Medium type is not enabled for organizer.'),
+            Checkin.REASON_ERROR,
+            reason=_('Medium type is not enabled for organizer.'),
+        )
+
+    if link_orderposition.item.media_type != media_type:
+        raise CheckInError(
+            _('Incorrect medium type for product.'),
+            Checkin.REASON_PRODUCT,
+            reason=_('Incorrect medium type for product.'),
+        )
+
+    if link_orderposition.linked_media.exists():
+        raise CheckInError(
+            _('Ticket is already exchanged for reusable medium.'),
+            Checkin.REASON_ALREADY_EXCHANGED,
+            reason=_('Ticket is already exchanged for reusable medium.'),
+        )
+
+    if media_policy == Item.MEDIA_POLICY_REUSE:
+        try:
+            medium = ReusableMedium.objects.get(
+                type=media_type,
+                identifier=identifier,
+                organizer=organizer,
+            )
+        except ReusableMedium.DoesNotExist:
+            raise CheckInError(
+                _('Reusable medium not found.'),
+                Checkin.REASON_MEDIUM_INVALID,
+            )
+
     elif media_policy == Item.MEDIA_POLICY_REUSE_OR_NEW:
         medium, created = ReusableMedium.objects.get_or_create(
             type=media_type,
@@ -117,7 +153,10 @@ def perform_media_exchange(organizer, media_type, identifier, link_action, link_
                 organizer=organizer,
             )
         except IntegrityError:
-            raise ReusableMedium.DuplicateEntry()
+            raise CheckInError(
+                _('Reusable medium already exists.'),
+                Checkin.REASON_MEDIUM_EXISTS,
+            )
         else:
             medium.log_action(
                 'pretix.reusable_medium.created.auto',
@@ -125,6 +164,13 @@ def perform_media_exchange(organizer, media_type, identifier, link_action, link_
                 auth=auth,
             )
 
+    else:
+        raise CheckInError(
+            _('Product does not support medium exchange.'),
+            Checkin.REASON_PRODUCT,
+            reason=_('Product does not support medium exchange.'),
+        )
+
     if link_action == 'append':
         medium.linked_orderpositions.add(link_orderposition)
     elif link_action == 'replace':

src/tests/api/test_checkinrpc.py

@@ -34,7 +34,7 @@ from tests.const import SAMPLE_PNG
 
 from pretix.api.serializers.item import QuestionSerializer
 from pretix.base.models import (
-    Checkin, InvoiceAddress, Order, OrderPosition, ReusableMedium,
+    Checkin, InvoiceAddress, Item, Order, OrderPosition, ReusableMedium,
 )
 
 # Lots of this code is overlapping with test_checkin.py, and some of it is arguably redundant since it's triggering
@@ -1253,3 +1253,397 @@ def test_annul_failures(device_client, team, organizer, clist, clist_event2, eve
     with scopes_disabled():
         ci = p.all_checkins.get()
         assert ci.successful
+
+
+@pytest.mark.django_db
+def test_exchange_incomplete_body(token_client, organizer, clist, event, order):
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid"
+    })
+    assert resp.status_code == 400
+    assert resp.data == {
+        'non_field_errors': ['If you set any of exchange_medium_type, exchange_medium_identifier, or '
+                             'exchange_link_action, you need to set all of them.']
+    }
+
+
+@pytest.mark.django_db
+def test_exchange_medium_for_medium(token_client, organizer, clist, event, order):
+    with scopes_disabled():
+        rm = ReusableMedium.objects.create(
+            type="barcode",
+            identifier="abcdef",
+            organizer=organizer,
+        )
+        rm.linked_orderpositions.add(order.positions.first())
+    resp = _redeem(token_client, organizer, clist, "abcdef", {
+        "source_type": "barcode",
+        "exchange_medium_type": "barcode",
+        "exchange_medium_identifier": "hijkl",
+        "exchange_link_action": "replace",
+    })
+    assert resp.status_code == 400
+    assert resp.data['status'] == 'error'
+    assert resp.data['reason'] == 'error'
+
+
+@pytest.mark.django_db
+def test_exchange_unknown_media_type(token_client, organizer, clist, event, order):
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "unknown",
+        "exchange_medium_identifier": "hijkl",
+        "exchange_link_action": "replace",
+    })
+    assert resp.status_code == 400
+    assert resp.data == {"exchange_medium_type": ["\"unknown\" is not a valid choice."]}
+
+
+@pytest.mark.django_db
+def test_exchange_disabled_media_type(token_client, organizer, clist, event, order):
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "hijkl",
+        "exchange_link_action": "replace",
+    })
+    assert resp.status_code == 400
+    assert resp.data['status'] == 'error'
+    assert resp.data['reason'] == 'error'
+    assert resp.data['reason_explanation'] == 'Medium type is not enabled for organizer.'
+
+
+@pytest.mark.django_db
+def test_exchange_mismatch_media_type(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "barcode"
+    item.save()
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "12345678",
+        "exchange_link_action": "replace",
+    })
+    assert resp.status_code == 400
+    assert resp.data['status'] == 'error'
+    assert resp.data['reason'] == 'product'
+    assert resp.data['reason_explanation'] == 'Incorrect medium type for product.'
+
+
+@pytest.mark.django_db
+def test_exchange_no_item_policy(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "nfc_uid"
+    item.save()
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "12345678",
+        "exchange_link_action": "replace",
+    })
+    assert resp.status_code == 400
+    assert resp.data['status'] == 'error'
+    assert resp.data['reason'] == 'product'
+    assert resp.data['reason_explanation'] == 'Product does not support medium exchange.'
+
+
+@pytest.mark.django_db
+def test_exchange_reuse_or_new_new(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_NEW
+    item.save()
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "12345678",
+        "exchange_link_action": "replace",
+    })
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+    with scopes_disabled():
+        rm = ReusableMedium.objects.get(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        assert rm.linked_orderpositions.get().secret == "z3fsn8jyufm5kpk768q69gkbyr5f4h6w"
+
+
+@pytest.mark.django_db
+def test_exchange_reuse_or_new_reuse_replace(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_REUSE_OR_NEW
+    item.save()
+    with scopes_disabled():
+        rm = ReusableMedium.objects.create(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        rm.linked_orderpositions.add(order.positions.last())
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "12345678",
+        "exchange_link_action": "replace",
+    })
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+    rm.refresh_from_db()
+    with scopes_disabled():
+        assert rm.linked_orderpositions.get().secret == "z3fsn8jyufm5kpk768q69gkbyr5f4h6w"
+
+
+@pytest.mark.django_db
+def test_exchange_reuse_or_new_reuse_append(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_REUSE_OR_NEW
+    item.save()
+    with scopes_disabled():
+        rm = ReusableMedium.objects.create(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        rm.linked_orderpositions.add(order.positions.last())
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "12345678",
+        "exchange_link_action": "append",
+    })
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+    rm.refresh_from_db()
+    with scopes_disabled():
+        assert rm.linked_orderpositions.count() == 2
+        assert rm.linked_orderpositions.filter(secret="z3fsn8jyufm5kpk768q69gkbyr5f4h6w").exists()
+
+
+@pytest.mark.django_db
+def test_exchange_reuse_exists_append(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_REUSE_OR_NEW
+    item.save()
+    with scopes_disabled():
+        rm = ReusableMedium.objects.create(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        rm.linked_orderpositions.add(order.positions.last())
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "12345678",
+        "exchange_link_action": "append",
+    })
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+    rm.refresh_from_db()
+    with scopes_disabled():
+        assert rm.linked_orderpositions.count() == 2
+        assert rm.linked_orderpositions.filter(secret="z3fsn8jyufm5kpk768q69gkbyr5f4h6w").exists()
+
+
+@pytest.mark.django_db
+def test_exchange_reuse_not_exists(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_REUSE
+    item.save()
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "12345678",
+        "exchange_link_action": "replace",
+    })
+    assert resp.status_code == 400
+    assert resp.data['status'] == 'error'
+    assert resp.data['reason'] == 'medium_invalid'
+
+
+@pytest.mark.django_db
+def test_exchange_new_exists(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_NEW
+    item.save()
+    with scopes_disabled():
+        rm = ReusableMedium.objects.create(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        rm.linked_orderpositions.add(order.positions.last())
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "12345678",
+        "exchange_link_action": "append",
+    })
+    assert resp.status_code == 400
+    assert resp.data['status'] == 'error'
+    assert resp.data['reason'] == 'medium_exists'
+
+
+@pytest.mark.django_db
+def test_exchange_new_not_exists(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_NEW
+    item.save()
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "12345678",
+        "exchange_link_action": "replace",
+    })
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+    with scopes_disabled():
+        rm = ReusableMedium.objects.get(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        assert rm.linked_orderpositions.get().secret == "z3fsn8jyufm5kpk768q69gkbyr5f4h6w"
+
+
+@pytest.mark.django_db
+def test_exchange_required(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_NEW
+    item.save()
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+    })
+    assert resp.status_code == 400
+    assert resp.data['status'] == 'exchange'
+    assert resp.data['media_policy'] == 'new'
+    assert resp.data['media_type'] == 'nfc_uid'
+
+    with scopes_disabled():
+        rm = ReusableMedium.objects.create(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        rm.linked_orderpositions.add(order.positions.first())
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+    })
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+    # Force works
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "force": True,
+    })
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+
+
+@pytest.mark.django_db
+def test_exchanged_original_barcode_ok(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_NEW
+    item.save()
+
+    with scopes_disabled():
+        rm = ReusableMedium.objects.create(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        rm.linked_orderpositions.add(order.positions.first())
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+    })
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+
+
+@pytest.mark.django_db
+def test_exchanged_original_barcode_not_ok(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    organizer.settings.reusable_media_usage_enforced = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_NEW
+    item.save()
+
+    with scopes_disabled():
+        rm = ReusableMedium.objects.create(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        rm.linked_orderpositions.add(order.positions.first())
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+    })
+    assert resp.status_code == 400
+    assert resp.data['status'] == 'error'
+    assert resp.data['reason'] == 'already_exchanged'
+    # Force works
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "force": True,
+    })
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+
+
+@pytest.mark.django_db
+def test_exchanged_scan_medium_ok(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    organizer.settings.reusable_media_usage_enforced = True
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_NEW
+    item.save()
+
+    with scopes_disabled():
+        rm = ReusableMedium.objects.create(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        rm.linked_orderpositions.add(order.positions.first())
+    resp = _redeem(token_client, organizer, clist, "12345678", {
+        "source_type": "nfc_uid",
+    })
+    assert resp.status_code == 201
+    assert resp.data['status'] == 'ok'
+
+
+@pytest.mark.django_db
+def test_exchanged_double_exchange(token_client, organizer, clist, event, order, item):
+    organizer.settings.reusable_media_type_nfc_uid = True
+    organizer.settings.reusable_media_usage_enforced = False
+    item.media_type = "nfc_uid"
+    item.media_policy = Item.MEDIA_POLICY_NEW
+    item.save()
+
+    with scopes_disabled():
+        rm = ReusableMedium.objects.create(
+            type="nfc_uid",
+            identifier="12345678",
+            organizer=organizer,
+        )
+        rm.linked_orderpositions.add(order.positions.first())
+    resp = _redeem(token_client, organizer, clist, "z3fsn8jyufm5kpk768q69gkbyr5f4h6w", {
+        "source_type": "barcode",
+        "exchange_medium_type": "nfc_uid",
+        "exchange_medium_identifier": "87654321",
+        "exchange_link_action": "replace",
+    })
+    assert resp.status_code == 400
+    assert resp.data['status'] == 'error'
+    assert resp.data['reason'] == 'already_exchanged'