Is needed to add an action.
When an issued invoice is cancelled, there can be two reasons:
1. The customer does not accept the invoice and returns the products received
2. The customer does not accept the invoice, but does want the products (all or some)
In the first case, the action contemplated in Tryton is logical: issuance of a new invoice (of the opposite sign), which maintains relations with the original sale, that is to say, when we consult the sale we will see that it has remained related to the first invoice and also to the opposite sign invoice.
But in the second case it can happen that the customer rejects the invoice due to a formal defect (for example: does not accept the date of issue). Then you also need to make a opposite sign invoice, but in addition, you need to issue another new correct invoice. Tryton then does not allow us to link a third invoice to the sale. It would be desirable to be able to relate it, because it is the culmination of the same original sale.
Dear Cédric
I could quote you a few silly reasons from the Spanish public administration.