[ADD] finance: explain how to disable online invoice payment

closes odoo/documentation#3383

Related: odoo/odoo#110177
Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>

content/applications/finance/accounting/receivables/customer_payments/online_payment.rst

@@ -1,7 +1,13 @@
+:show-content:
+
 ======================
 Invoice online payment
 ======================
 
+.. toctree::
+
+   online_payment/install_portal_patch
+
 To make it more convenient for your customers to pay the invoices you issue, you can activate the
 **Invoice Online Payment** feature, which adds a *Pay Now* button on their **Customer Portal**. This
 allows your customers to see their invoices online and pay directly with their favorite payment

content/applications/finance/accounting/receivables/customer_payments/online_payment/install_portal_patch.rst

@@ -0,0 +1,57 @@
+===================================================
+Install the patch to disable online invoice payment
+===================================================
+
+Following recent changes in Odoo 16, you might be warned that disabling the :guilabel:`Invoice
+Online Payment` setting will uninstall modules. If you want to disable the feature without
+uninstalling modules, follow the steps below to install the module **Payment - Account / Invoice
+Online Payment Patch**.
+
+.. note::
+   | If your Odoo database is created after the module **Payment - Account / Invoice Online Payment
+     Patch** was released, you don't have anything to do.
+   | To check if the module is already installed, go to :guilabel:`Apps`, remove the `Apps` filter,
+     and search for `account_payment`. If the module **Payment - Account / Invoice Online Payment
+     Patch** is present and marked as installed, your Odoo database is already up-to-date and you
+     are able to disable the feature without side-effect.
+
+Update Odoo to the latest release
+=================================
+
+The possibility to disable the :guilabel:`Invoice Online Payment` setting without side-effect is
+made available through a new Odoo module; to be able to install it, you must make sure that your
+Odoo source code is up-to-date.
+
+If you use Odoo on Odoo.com or Odoo.sh platform, your code is already up-to-date and you can proceed
+to the next step.
+
+If you use Odoo with an on-premise setup or through a partner, you must update your installation as
+detailed in :doc:`this documentation page </administration/maintain/update>`, or by contacting your
+integrating partner.
+
+Update the list of available modules
+====================================
+
+New modules must be *discovered* by your Odoo instance to be available in the **Apps** menu.
+
+To do so, activate the :ref:`developer mode <developer-mode>`, and go to :menuselection:`Apps -->
+Update Apps List`. A wizard will ask for confirmation.
+
+Install the module Invoice Online Payment Patch
+===============================================
+
+.. warning::
+   You should never install new modules in your production database without first testing them in a
+   duplicate or staging environment. For Odoo.com customers, a duplicate database can be created
+   from the database management page. For Odoo.sh users, you should use a staging or duplicate
+   database. For on-premise users, you should use a staging environment---contact your integrating
+   partner for more information regarding how to test a new module in your particular setup.
+
+The module should now be available in your :guilabel:`Apps` menu. Remove the ``Apps`` filter and
+search for ``account_payment``; the module :guilabel:`Payment - Account / Invoice Online Payment Patch`
+should be available for installation. If you cannot find the module after having updated the list
+of available modules, it means your Odoo source code is not up-to-date; refer to step one of this
+page.
+
+Once the module is installed, disabling the feature will work as intended and will not ask you to
+uninstall installed applications or modules.