fix(accounts): keep paid amount in payment term outstanding on update items

erpnext/accounts/services/payment_schedule.py

@@ -92,6 +92,7 @@ class PaymentScheduleService:
 			and allocate_payment_based_on_payment_terms
 			and self.linked_order_has_payment_terms(po_or_so, fieldname, doctype)
 		):
+			keep_settled = doc.docstatus == 1 and getattr(doc, "_action", None) != "submit"
 			for d in doc.get("payment_schedule"):
 				if d.invoice_portion:
 					d.payment_amount = flt(
@@ -100,20 +101,30 @@ class PaymentScheduleService:
 					d.base_payment_amount = flt(
 						base_grand_total * flt(d.invoice_portion) / 100, d.precision("base_payment_amount")
 					)
-					d.outstanding = d.payment_amount
-					d.base_outstanding = d.base_payment_amount
 				elif not d.invoice_portion:
 					d.base_payment_amount = flt(
 						d.payment_amount * doc.get("conversion_rate"), d.precision("base_payment_amount")
 					)
-					d.outstanding = d.payment_amount
-					d.base_outstanding = d.base_payment_amount
+				self.set_term_outstanding(d, keep_settled)
 		else:
 			self.fetch_payment_terms_from_order(
 				po_or_so, doctype, grand_total, base_grand_total, automatically_fetch_payment_terms
 			)
 			doc.ignore_default_payment_terms_template = 1
 
+	def set_term_outstanding(self, term, keep_settled: bool) -> None:
+		settled = base_settled = 0
+		if keep_settled:
+			settled = flt(term.paid_amount) + flt(term.discounted_amount)
+			base_settled = flt(term.base_paid_amount) + flt(term.discounted_amount) * flt(
+				self.doc.get("conversion_rate")
+			)
+
+		term.outstanding = flt(term.payment_amount - settled, term.precision("outstanding"))
+		term.base_outstanding = flt(
+			term.base_payment_amount - base_settled, term.precision("base_outstanding")
+		)
+
 	def get_order_details(self) -> tuple:
 		doc = self.doc
 		if not doc.get("items"):