not enough balance error

apps/wallet/models.py

@@ -67,6 +67,8 @@ class Transaction(models.Model):
 
     def withdraw_from_payer_balance(self):
         payer = self.get_payer()
+        if self.amount > payer.balance:
+            raise APIException('not enough balance')
         payer.balance = F('balance') - self.amount
         payer.save(update_fields=['balance'])