API: Allow to add a fee to an order (#4806) (#4829)

* API: Allow to add a fee to an order (#4806)

* Fix example in docs

* Consistent order of examples

* Add create_fees to example

* docs: None -> null

* docs: update fee_type options

---------

Co-authored-by: Mira Weller <weller@rami.io>

src/pretix/api/views/order.py

@@ -63,7 +63,8 @@ from pretix.api.serializers.order import (
 )
 from pretix.api.serializers.orderchange import (
     BlockNameSerializer, OrderChangeOperationSerializer,
-    OrderFeeChangeSerializer, OrderPositionChangeSerializer,
+    OrderFeeChangeSerializer, OrderFeeCreateForExistingOrderSerializer,
+    OrderPositionChangeSerializer,
     OrderPositionCreateForExistingOrderSerializer,
     OrderPositionInfoPatchSerializer,
 )
@@ -988,6 +989,12 @@ class EventOrderViewSet(OrderViewSetMixin, viewsets.ModelViewSet):
                 ocm.cancel_fee(r['fee'])
                 canceled_fees.add(r['fee'])
 
+            for r in serializer.validated_data.get('create_fees', []):
+                pos_serializer = OrderFeeCreateForExistingOrderSerializer(
+                    context={'ocm': ocm, 'commit': False, 'event': request.event, **self.get_serializer_context()},
+                )
+                pos_serializer.create(r)
+
             for r in serializer.validated_data.get('patch_fees', []):
                 if r['fee'] in canceled_fees:
                     continue