#4 fix payment registration

membership_payment_date/models/account_move.py

@@ -53,14 +53,24 @@ class AccountMove(models.Model):
         return res
 
     def _get_membership_payment_date(self, invoice):
-        """Get the date of the most recent reconciled payment.
+        """Get the date of the most recent payment reconciled with the invoice.
 
-        If there are no payments (e.g. zero-amount invoice), fallback to today.
+        Uses the ``_get_reconciled_payments()`` helper instead of the
+        ``reconciled_payment_ids`` field: that field was dropped in 18.0 and
+        only reintroduced on 2025-10-13 (odoo/odoo d8e7798d2c), so it is
+        missing on older 18.0 builds. ``matched_payment_ids`` is not an option
+        either: the register wizard links it *after* reconciling, so it is
+        still empty when ``_invoice_paid_hook`` runs.
+
+        If nothing is reconciled (e.g. zero-amount invoice), fallback to today.
         """
-        self.ensure_one()
-        payments = invoice.reconciled_payment_ids
+        payments = invoice._get_reconciled_payments()
         if payments:
             return max(payments.mapped("date"))
+        # Counterparts that are not payments: credit notes, manual entries...
+        reconciled_amls = invoice._get_reconciled_amls()
+        if reconciled_amls:
+            return max(reconciled_amls.mapped("date"))
         return fields.Date.today()
 
     def _compute_membership_dates(

membership_payment_date/tests/test_membership_payment_date.py

@@ -110,6 +110,15 @@ class TestMembershipPaymentDate(common.TransactionCase):
             }
         )
         cls.product_variable = template_variable.product_variant_id
+        # Plain service, not a membership
+        template_service = cls.env["product.template"].create(
+            {
+                "name": "Consulting Service",
+                "type": "service",
+                "list_price": 50.0,
+            }
+        )
+        cls.product_service = template_service.product_variant_id
 
     def _create_invoice(self, product, invoice_date, quantity=1.0):
         """Create and return a draft out_invoice with the given product."""
@@ -311,3 +320,40 @@ class TestMembershipPaymentDate(common.TransactionCase):
         self._register_payment(invoice, payment_date=date(2026, 5, 10))
         self.assertEqual(mline.date_from, date(2026, 5, 10))
         self.assertEqual(mline.date_to, date(2026, 12, 31))
+
+    def test_09_single_payment_for_several_invoices(self):
+        """One payment settling several invoices at once.
+
+        The reconciliation calls _invoice_paid_hook with a multi-record
+        recordset, which used to raise "Expected singleton".
+        """
+        membership_invoice = self._create_invoice(
+            self.product_fixed, invoice_date=date(2026, 5, 1)
+        )
+        mline = self._post_invoice(membership_invoice)[0]
+        other_invoice = self._create_invoice(
+            self.product_service, invoice_date=date(2026, 5, 1)
+        )
+        other_invoice.action_post()
+        invoices = membership_invoice | other_invoice
+        payment_register = (
+            self.env["account.payment.register"]
+            .with_context(
+                active_model="account.move",
+                active_ids=invoices.ids,
+            )
+            .create(
+                {
+                    "payment_date": date(2026, 5, 10),
+                    "journal_id": self.bank_journal.id,
+                    "group_payment": True,
+                }
+            )
+        )
+        payment_register._create_payments()
+        self.assertTrue(
+            all(inv.payment_state in ("paid", "in_payment") for inv in invoices)
+        )
+        # The membership line still gets the payment date, not today's date
+        self.assertEqual(mline.date_from, date(2026, 5, 10))
+        self.assertEqual(mline.date_to, date(2026, 12, 31))