diff --git a/addons/website_portal_sale/models/payment.py b/addons/website_portal_sale/models/payment.py
index 7aa838149bd..fcc4aa09a40 100644
--- a/addons/website_portal_sale/models/payment.py
+++ b/addons/website_portal_sale/models/payment.py
@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 import logging
-from odoo import api, fields, models
+from odoo import _, api, fields, models
 from odoo.tools import float_compare
 
 _logger = logging.getLogger(__name__)
@@ -80,4 +80,16 @@ class PaymentTransaction(models.Model):
                         _logger.info('<%s> transaction pending/to confirm manually, sending quote email for order %s (ID %s)', acquirer_name, tx.sale_order_id.name, tx.sale_order_id.id)
                         tx.sale_order_id.force_quotation_send()
                 else:
-                    _logger.warning('<%s> transaction MISMATCH for order %s (ID %s)', acquirer_name, tx.sale_order_id.name, tx.sale_order_id.id)
+                    _logger.warning(
+                        '<%s> transaction AMOUNT MISMATCH for order %s (ID %s): expected %r, got %r',
+                        acquirer_name, tx.sale_order_id.name, tx.sale_order_id.id,
+                        tx.sale_order_id.amount_total, tx.amount,
+                    )
+                    tx.sale_order_id.message_post(
+                        subject=_("Amount Mismatch (%s)") % acquirer_name,
+                        body=_("The sale order was not confirmed despite response from the acquirer (%s): SO amount is %r but acquirer replied with %r.") % (
+                            acquirer_name,
+                            tx.sale_order_id.amount_total,
+                            tx.amount,
+                        )
+                    )