When creating a payment in Core, is it possible to search by invoice number in the Add Payment screen? It lists all the invoices of a project or client for payment, but user wants to search for a particular invoice to apply a payment to it.
You cannot search for a particular invoice in the Payments > Add Payment screen. However, an alternative to this is to make payments on invoices via the Invoices screen directly. Search for the relevant invoice there in the list view, then click on its row-action menu and select Create Payment. It takes you to the Add Payment screen with the relevant invoice selected. Check the Core Help for details.