Fix invoice generation flow

auction/models.py

@@ -37,8 +37,9 @@ class Inquiry(models.Model):
         return self.invoice.is_paid
 
     def process_payment(self):
-        self.activated = timezone.now()
-        self.save()
+        if self.invoice.is_paid:
+            self.activated = timezone.now()
+            self.save()
 
     @property
     def expiry(self):

payment/models.py

@@ -93,10 +93,13 @@ class Invoice(models.Model):
         return self.balance >= 0
 
     def finalize(self, *args, **kwargs):
-        try:
-            self.inquiry.process_payment(*args, **kwargs)
-        except Inquiry.DoesNotExist:
-            pass
+        if self.is_paid:
+            try:
+                self.inquiry.process_payment(*args, **kwargs)
+            except Inquiry.DoesNotExist:
+                pass
+
+            self.generate_invoice()
 
     def generate_invoice(self):
         output = BytesIO()