You left out one critical piece of information, @ProDev. Your third screen shot of purchase invoice INV-1659165 shows that you entered a debit note for ZOL Zimbabwe on 26 October. I can’t be absolutely certain from the information shown, but it looks like both that debit note and your 27 August payment were both posted specifically to INV-1659165. So it is overpaid.
Manager used to carry forward all overpayments to subsequent invoices, but no longer does so in order to avoid rolling changes. If a payment or debit note is posted specifically to an invoice, it remains tied only to that invoice. If you leave the invoice number field blank, Manager will still roll supplier credits forward to subsequent invoices. See https://www.manager.io/guides/12951 and https://www.manager.io/guides/10355.