diff --git a/dlv_account_move_copy_ref/CHANGELOG.md b/dlv_account_move_copy_ref/CHANGELOG.md
new file mode 100644
index 0000000..a6f1baf
--- /dev/null
+++ b/dlv_account_move_copy_ref/CHANGELOG.md
@@ -0,0 +1,15 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [16.0.1.0.0] - 2026-10-04
+
+### Added
+- Initial release.
+- `account.move.ref` is copied on duplicate for customer invoices and customer
+  credit notes (`out_invoice`, `out_refund`).
+- Warning dialog (OK to continue) after the Duplicate action when the copied reference has
+  a value.
diff --git a/dlv_account_move_copy_ref/README.md b/dlv_account_move_copy_ref/README.md
new file mode 100644
index 0000000..91b39ff
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+++ b/dlv_account_move_copy_ref/README.md
@@ -0,0 +1,38 @@
+# dlv_account_move_copy_ref
+
+## Overview
+
+In core Odoo the reference of an invoice (`account.move.ref`, label
+**Customer Reference** on customer documents) is not copied when the invoice is
+duplicated. This addon makes it copy, and warns the user afterwards.
+
+## How it works
+
+- **Python** (`models/account_move.py`): `ref` gets `copy=True`. `copy_data()`
+  removes it again for every move that is not `out_invoice` / `out_refund`, so
+  vendor bills and journal entries keep the core behaviour. An explicit `ref`
+  in the `default` dict always wins (credit note reversal sets its own).
+- **JS** (`static/src/js/duplicate_warning.js`): patches
+  `FormController.duplicateRecord`. After the duplicate, if the new record is an
+  `account.move` customer invoice/credit note with a non-empty `ref`, a modal alert dialog (OK button)
+  warning is shown: "'Customer Reference' was also copied, check
+  whether it is still relevant or should be removed." (nl: "'Referentie klant'
+  werd ook gekopieerd, kijk na of dit relevant is of dient verwijderd te
+  worden.")
+
+## Scope
+
+- Only the Duplicate action in the form view shows the warning. Server-side
+  `copy()` calls (e.g. recurring entries) copy the reference silently.
+- No warning when `ref` is empty.
+
+## Compatibility
+
+- Odoo 16.0 (Community and Enterprise)
+- Depends on: `account`
+
+## Credits
+
+bv Domus La Vila — https://domuslavila.eu
+
+License: LGPL-3
diff --git a/dlv_account_move_copy_ref/__init__.py b/dlv_account_move_copy_ref/__init__.py
new file mode 100644
index 0000000..0650744
--- /dev/null
+++ b/dlv_account_move_copy_ref/__init__.py
@@ -0,0 +1 @@
+from . import models
diff --git a/dlv_account_move_copy_ref/__manifest__.py b/dlv_account_move_copy_ref/__manifest__.py
new file mode 100644
index 0000000..e2efb77
--- /dev/null
+++ b/dlv_account_move_copy_ref/__manifest__.py
@@ -0,0 +1,32 @@
+# -*- coding: utf-8 -*-
+{
+    "name": "DLV Account Move Copy Ref",
+    "summary": "Copy the customer reference when duplicating a customer "
+               "invoice or credit note, and warn about it",
+    "description": """
+By default the reference (account.move.ref, shown as "Customer Reference")
+is not copied when an invoice is duplicated.
+
+This addon copies it for customer invoices and customer credit notes
+(out_invoice, out_refund). Vendor bills and journal entries are unchanged.
+
+After the Duplicate action in the form view, a warning dialog is shown
+when the copied reference has a value, so the user can check whether it is
+still relevant or has to be removed.
+""",
+    "author": "bv Domus La Vila",
+    "website": "https://domuslavila.eu",
+    "category": "Accounting/Accounting",
+    "version": "16.0.1.0.0",
+    "license": "LGPL-3",
+    "depends": ["account"],
+    "data": [],
+    "assets": {
+        "web.assets_backend": [
+            "dlv_account_move_copy_ref/static/src/js/duplicate_warning.js",
+        ],
+    },
+    "installable": True,
+    "application": False,
+    "auto_install": False,
+}
diff --git a/dlv_account_move_copy_ref/i18n/nl.po b/dlv_account_move_copy_ref/i18n/nl.po
new file mode 100644
index 0000000..204c9c9
--- /dev/null
+++ b/dlv_account_move_copy_ref/i18n/nl.po
@@ -0,0 +1,31 @@
+# Translation of Odoo Server.
+# This file contains the translation of the following modules:
+# 	* dlv_account_move_copy_ref
+#
+msgid ""
+msgstr ""
+"Project-Id-Version: Odoo Server 16.0\n"
+"Report-Msgid-Bugs-To: \n"
+"Language: nl\n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+#. module: dlv_account_move_copy_ref
+#. odoo-javascript
+#: code:addons/dlv_account_move_copy_ref/static/src/js/duplicate_warning.js:0
+#, python-format
+msgid ""
+"'Customer Reference' was also copied, check whether it is still relevant or "
+"should be removed. You can find it under the 'Other Info' tab."
+msgstr ""
+"'Referentie klant' werd ook gekopieerd, kijk na of dit relevant is of dient "
+"verwijderd te worden. Je vindt dit onder tab 'Overige info'."
+
+#. module: dlv_account_move_copy_ref
+#. odoo-javascript
+#: code:addons/dlv_account_move_copy_ref/static/src/js/duplicate_warning.js:0
+#, python-format
+msgid "Warning"
+msgstr "Waarschuwing"
diff --git a/dlv_account_move_copy_ref/i18n/nl_BE.po b/dlv_account_move_copy_ref/i18n/nl_BE.po
new file mode 100644
index 0000000..db0506c
--- /dev/null
+++ b/dlv_account_move_copy_ref/i18n/nl_BE.po
@@ -0,0 +1,31 @@
+# Translation of Odoo Server.
+# This file contains the translation of the following modules:
+# 	* dlv_account_move_copy_ref
+#
+msgid ""
+msgstr ""
+"Project-Id-Version: Odoo Server 16.0\n"
+"Report-Msgid-Bugs-To: \n"
+"Language: nl_BE\n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+#. module: dlv_account_move_copy_ref
+#. odoo-javascript
+#: code:addons/dlv_account_move_copy_ref/static/src/js/duplicate_warning.js:0
+#, python-format
+msgid ""
+"'Customer Reference' was also copied, check whether it is still relevant or "
+"should be removed. You can find it under the 'Other Info' tab."
+msgstr ""
+"'Referentie klant' werd ook gekopieerd, kijk na of dit relevant is of dient "
+"verwijderd te worden. Je vindt dit onder tab 'Overige info'."
+
+#. module: dlv_account_move_copy_ref
+#. odoo-javascript
+#: code:addons/dlv_account_move_copy_ref/static/src/js/duplicate_warning.js:0
+#, python-format
+msgid "Warning"
+msgstr "Waarschuwing"
diff --git a/dlv_account_move_copy_ref/models/__init__.py b/dlv_account_move_copy_ref/models/__init__.py
new file mode 100644
index 0000000..9c0a421
--- /dev/null
+++ b/dlv_account_move_copy_ref/models/__init__.py
@@ -0,0 +1 @@
+from . import account_move
diff --git a/dlv_account_move_copy_ref/models/account_move.py b/dlv_account_move_copy_ref/models/account_move.py
new file mode 100644
index 0000000..a9cd301
--- /dev/null
+++ b/dlv_account_move_copy_ref/models/account_move.py
@@ -0,0 +1,20 @@
+from odoo import fields, models
+
+CUSTOMER_MOVE_TYPES = ("out_invoice", "out_refund")
+
+
+class AccountMove(models.Model):
+    _inherit = "account.move"
+
+    # Core has copy=False. Flipped to True here; copy_data() below limits the
+    # effect to customer invoices and credit notes.
+    ref = fields.Char(copy=True)
+
+    def copy_data(self, default=None):
+        data_list = super().copy_data(default)
+        if default and "ref" in default:
+            return data_list
+        for move, data in zip(self, data_list):
+            if move.move_type not in CUSTOMER_MOVE_TYPES:
+                data.pop("ref", None)
+        return data_list
diff --git a/dlv_account_move_copy_ref/static/src/js/duplicate_warning.js b/dlv_account_move_copy_ref/static/src/js/duplicate_warning.js
new file mode 100644
index 0000000..34a8feb
--- /dev/null
+++ b/dlv_account_move_copy_ref/static/src/js/duplicate_warning.js
@@ -0,0 +1,34 @@
+/** @odoo-module **/
+
+import { patch } from "@web/core/utils/patch";
+import { FormController } from "@web/views/form/form_controller";
+import { AlertDialog } from "@web/core/confirmation_dialog/confirmation_dialog";
+
+const CUSTOMER_MOVE_TYPES = ["out_invoice", "out_refund"];
+
+patch(FormController.prototype, "dlv_account_move_copy_ref", {
+    async duplicateRecord() {
+        await this._super(...arguments);
+        const root = this.model.root;
+        if (
+            root.resModel === "account.move" &&
+            CUSTOMER_MOVE_TYPES.includes(root.data.move_type) &&
+            root.data.ref
+        ) {
+            await new Promise((resolve) => {
+                this.env.services.dialog.add(
+                    AlertDialog,
+                    {
+                        title: this.env._t("Warning"),
+                        body: this.env._t(
+                            "'Customer Reference' was also copied, check whether it is " +
+                                "still relevant or should be removed. You can find it " +
+                                "under the 'Other Info' tab."
+                        ),
+                    },
+                    { onClose: resolve }
+                );
+            });
+        }
+    },
+});