I run an event organisation company

for legal reasons every booth that we sell we first have to invoice 50% before the event starts

and then 50% after the event is finished.

We use odoo's feature to generate the 50% invoices. When you have a sale order open you can click on generate invoice and select invoice Down payment (percentage)

We then put 50% each time.

Now I have a customer which has already paid both invoices but we still need to cancel and refund the invoice and money 

How do I get an invoice that cancels both in one go?

Because if I cancel each one individually I get two invoices but I need one that cancels both


thank you for your support

odoo15