Zoho Books - sum of previous invoices plus the actual amount of the recent invoice in one Number.

Zoho Books - sum of previous invoices plus the actual amount of the recent invoice in one Number.

In Book you have "sales" and there you can issue a retainer invoice.
As we are in construction business we issue plenty of retainer invoices for a project until at the very end we issue ONE INVOICE.

According to german tax requirements we have to follow certain forms for these retainer invoices.
The template in Zoho is useful but we have add a field in every new retainer that sums up the amounts we invoices in previous retainer.

So in other words, we have to invoice the sum of previous invoices plus the actual amount of the recent invoice in one Number. Then we say "amount already paid" - that amount will be deducted from the total amount so we have a balance that is due with the recent invoice.