I see no navigation control on your subform so there's really no way to navigate from one payment to another for a given invoice. Either enable or switch to a datasheet for the subform. You need InvoiceID on the main form and the subform and set the Link Master & Child fields property for each invoice id control. If you use a combo to filter/find an invoice, don't bind the control (it should not have a recordsource property). Showing id values is ok when developing but usually they are not shown to users. If they are numbers and not meaningful data, those values mean nothing to the user and usually only add confusion.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.