[ADD] accounting: how to refund a payment

accounting/receivables/customer_invoices/refund.rst

@@ -1,3 +1,69 @@
 =================================
 How to edit or refund an invoice?
 =================================
+In Odoo, it's not possible to modify an invoice that has been validated
+and sent to the customer. If a mistake was made on a validated invoice,
+the legal way to handle that is to refund the invoice, reconcile it with
+the original invoice to close them and create a new invoice.
+
+Modifying a validated invoice
+=============================
+
+If you need to modify an existing invoice, use the Refund Invoice button
+on the invoice. In the refund method field, select "Modify: create a
+refund, reconcile, and create a new draft invoice".
+
+.. image:: ./media/image04.png
+   :align: center
+
+Odoo will automatically:
+
+-  Create a refund for your invoice
+-  Reconcile the refund invoice with the original invoice (marking both as Paid)
+-  Create a new draft invoice you can modify
+
+Then, you can modify the draft invoice and validate it once it's correct.
+
+Cancelling an invoice
+=====================
+
+If you need to cancel an existing invoice, use the Refund Invoice button
+on the invoice. In the refund method field, select "Cancel: create a
+refund and reconcile".
+
+.. image:: ./media/image05.png
+   :align: center
+
+Odoo will automatically:
+
+-  Create a refund for your invoice
+-  Reconcile the refund invoice with the original invoice (marking both as Paid)
+
+Nothing else needs to be done. You can send the refund by regular mail or email
+to your customer, if you already sent the original invoice.
+
+Refunding part of an invoice
+============================
+
+If you need to refund an existing invoice partially, use the Refund
+Invoice button on the invoice. In the refund method field, select
+"Create a draft refund".
+
+.. image:: ./media/image03.png
+   :align: center
+
+Odoo will automatically create a draft refund. You may modify the refund
+(example: remove the lines you do not want to refund) and validate it.
+Then, send the refund by regular mail or email to your customer.
+
+.. tip::
+
+	Refunding an invoice is different from refunding a payment. Usually, a
+	refund invoice is sent before the customer has done a payment. If the
+	customer has already paid, they should be reimbursed by doing a customer
+	payment refund. See :doc:`../customer_payments/refund`
+
+.. rst-class:: text-muted
+
+| Written by Fabien Pinckaers (Odoo)
+| Proofread by Johan Bosma (Onestein)