Make partial invoice for delivery note

our customers procedure is to split invoicing for a particular delivery.

E.g.: Delivery Note amount of shipped products is 10.000,-.
But they want to create two invoices for two payment, first invoice 9.000,-, second invoice for 1.000,-. A Delivery is only a partial Sales Order, so invoicing must be done based on delivery.

Because taxes need to be paid in the month of invoice and the second payment is a couple months later (after commissioning, testing etc.), the customer wants to split payment into two distinct invoices. So a simple payment schedule doesn’t work here because of tax regulations, it’s rather an “invoice schedule”.

Does anyone know a solution for this problem? I welcome any idea.

If someone else is looking for a partial invoice solution which is pretty neat even though ERPNext does not implement it natively: