diff --git a/core/apps/orders/serializers/party.py b/core/apps/orders/serializers/party.py
index 97160e6..a31baaf 100644
--- a/core/apps/orders/serializers/party.py
+++ b/core/apps/orders/serializers/party.py
@@ -352,8 +352,8 @@ class PartyUpdateSerializer(serializers.ModelSerializer):
             )
             party_amount = PartyAmount.objects.get(party=instance)
             party_amount.total_price = total_price
-            party_amount.cost_amount = total_price - party.discount
-            party_amount.payment_amount = total_price - party.discount
+            party_amount.cost_amount = total_price - instance.discount
+            party_amount.payment_amount = total_price - instance.discount
             party_amount.save()
             return instance