[FIX] sale_advance_payment: Use signed amount when computing residuals

Otherwise, we might get incorrect residuals when we get refunds

sale_advance_payment/models/sale.py

@@ -81,7 +81,9 @@ def _compute_advance_payment(self):
             # Consider payments in related invoices.
             invoice_paid_amount = 0.0
             for inv in order.invoice_ids:
-                invoice_paid_amount += inv.amount_total - inv.amount_residual
+                invoice_paid_amount += (
+                    inv.amount_total_signed - inv.amount_residual_signed
+                )
             amount_residual = order.amount_total - advance_amount - invoice_paid_amount
             payment_state = "not_paid"
             if mls:

sale_advance_payment/tests/test_sale_advance_payment.py

@@ -371,3 +371,33 @@ def test_03_residual_amount_big_pre_payment(self):
         self.assertEqual(invoice.amount_residual, 0.0)
         self.assertEqual(self.sale_order_1.amount_residual, 1600)
         self.assertEqual(invoice.amount_residual, 0)
+
+    def test_04_refunds(self):
+        self.assertEqual(
+            self.sale_order_1.amount_residual,
+            3600,
+        )
+        self.sale_order_1.action_confirm()
+        invoice = self.sale_order_1._create_invoices()
+        invoice.action_post()
+        self.assertEqual(invoice.amount_total, 3600)
+        self.assertEqual(
+            self.sale_order_1.amount_residual,
+            3600,
+        )
+        self.env["account.move.reversal"].with_context(
+            active_model="account.move", active_ids=invoice.ids
+        ).create({"journal_id": invoice.journal_id.id}).reverse_moves()
+        self.assertEqual(len(self.sale_order_1.invoice_ids), 2)
+        invoice = self.sale_order_1.invoice_ids.filtered(lambda x: x.state == "draft")
+        invoice.action_post()
+        self.assertEqual(
+            self.sale_order_1.amount_residual,
+            3600,
+        )
+        invoice = self.sale_order_1._create_invoices()
+        invoice.action_post()
+        self.assertEqual(
+            self.sale_order_1.amount_residual,
+            3600,
+        )