return validate attr in assignment serializer - import exclude param in organizations list

apps/pos_device/web/api/v1/serilaizers/device.py

@@ -59,6 +59,8 @@ class DeviceAssignmentSerializer(ModelSerializer):
         if self.Meta.model.objects.filter(device=device, client=client).exists():
             raise pos_exceptions.DeviceAlreadyAssigned()
 
+        return attrs
+
     def to_representation(self, instance):
         representation = super().to_representation(instance)