diff --git a/uncloud/uncloud_pay/management/commands/generate-bills.py b/uncloud/uncloud_pay/management/commands/generate-bills.py
index a7dbe78..5bd4519 100644
--- a/uncloud/uncloud_pay/management/commands/generate-bills.py
+++ b/uncloud/uncloud_pay/management/commands/generate-bills.py
@@ -9,8 +9,6 @@ from datetime import timedelta, date
 from django.utils import timezone
 from uncloud_pay.models import Bill
 
-BILL_PAYMENT_DELAY=timedelta(days=10)
-
 logger = logging.getLogger(__name__)
 
 class Command(BaseCommand):
@@ -31,8 +29,7 @@ class Command(BaseCommand):
             Bill.generate_for(
                     year=now.year,
                     month=now.month,
-                    user=user,
-                    allowed_delay=BILL_PAYMENT_DELAY)
+                    user=user)
 
         # We're done for this round :-)
         print("=> Done.")
diff --git a/uncloud/uncloud_pay/models.py b/uncloud/uncloud_pay/models.py
index 43064e4..32d3eac 100644
--- a/uncloud/uncloud_pay/models.py
+++ b/uncloud/uncloud_pay/models.py
@@ -180,6 +180,12 @@ class Bill(models.Model):
 
     valid = models.BooleanField(default=True)
 
+    @property
+    def reference(self):
+        return "{}_{}".format(
+                self.owner.username,
+                self.creation_date.strftime("%Y-%m-%d-%H%M"))
+
     @property
     def records(self):
         bill_records = []
diff --git a/uncloud/uncloud_pay/serializers.py b/uncloud/uncloud_pay/serializers.py
index aa75fd9..60ddc75 100644
--- a/uncloud/uncloud_pay/serializers.py
+++ b/uncloud/uncloud_pay/serializers.py
@@ -47,27 +47,6 @@ class CreatePaymentMethodSerializer(serializers.ModelSerializer):
         model = PaymentMethod
         fields = ['source', 'description', 'primary', 'credit_card']
 
-
-###
-# Bills
-
-# TODO: remove magic numbers for decimal fields
-class BillRecordSerializer(serializers.Serializer):
-    order = serializers.CharField()
-    description = serializers.CharField()
-    recurring_period = serializers.CharField()
-    recurring_price = serializers.DecimalField(max_digits=10, decimal_places=2)
-    recurring_count = serializers.DecimalField(max_digits=10, decimal_places=2)
-    one_time_price = serializers.DecimalField(max_digits=10, decimal_places=2)
-    amount = serializers.DecimalField(max_digits=10, decimal_places=2)
-
-class BillSerializer(serializers.ModelSerializer):
-    records = BillRecordSerializer(many=True, read_only=True)
-    class Meta:
-        model = Bill
-        fields = ['owner', 'total', 'due_date', 'creation_date',
-                'starting_date', 'ending_date', 'records', 'final']
-
 ###
 # Orders & Products.
 
@@ -83,3 +62,26 @@ class OrderSerializer(serializers.ModelSerializer):
         model = Order
         fields = ['uuid', 'creation_date', 'starting_date', 'ending_date',
                 'bill', 'recurring_period', 'records', 'recurring_price', 'one_time_price']
+
+
+###
+# Bills
+
+# TODO: remove magic numbers for decimal fields
+class BillRecordSerializer(serializers.Serializer):
+    order = serializers.HyperlinkedRelatedField(
+            view_name='order-detail',
+            read_only=True)
+    description = serializers.CharField()
+    recurring_period = serializers.CharField()
+    recurring_price = serializers.DecimalField(max_digits=10, decimal_places=2)
+    recurring_count = serializers.DecimalField(max_digits=10, decimal_places=2)
+    one_time_price = serializers.DecimalField(max_digits=10, decimal_places=2)
+    amount = serializers.DecimalField(max_digits=10, decimal_places=2)
+
+class BillSerializer(serializers.ModelSerializer):
+    records = BillRecordSerializer(many=True, read_only=True)
+    class Meta:
+        model = Bill
+        fields = ['reference', 'owner', 'total', 'due_date', 'creation_date',
+                'starting_date', 'ending_date', 'records', 'final']
diff --git a/uncloud/uncloud_pay/views.py b/uncloud/uncloud_pay/views.py
index 38d1aa4..57c284d 100644
--- a/uncloud/uncloud_pay/views.py
+++ b/uncloud/uncloud_pay/views.py
@@ -34,9 +34,6 @@ class BillViewSet(viewsets.ReadOnlyModelViewSet):
     def get_queryset(self):
         return Bill.objects.filter(owner=self.request.user)
 
-    def unpaid(self, request):
-        return Bill.objects.filter(owner=self.request.user, paid=False)
-
 class PaymentViewSet(viewsets.ReadOnlyModelViewSet):
     serializer_class = PaymentSerializer
     permission_classes = [permissions.IsAuthenticated]