fix: typeerror on invoice creation from SO/PO

(cherry picked from commit 9bd56b0f79)

erpnext/controllers/accounts_controller.py

@@ -1319,6 +1319,9 @@ class AccountsController(TransactionBase):
 				payment_schedule['discount_type'] = schedule.discount_type
 				payment_schedule['discount'] = schedule.discount
 
+			if not schedule.invoice_portion:
+				payment_schedule['payment_amount'] = schedule.payment_amount
+
 			self.append("payment_schedule", payment_schedule)
 
 	def set_due_date(self):