How to transfer articles from an invoice to another?

Let's say that Mario Pret's room will be added to Nathalie Rey's reservation.

Click then on Nathalie's reservation

Click on the number of the reservation

Copy this number. It is the ID of the invoice of Nathalie's reservation

Click on Calendar

And click on Mario's reservation

Click here

Click on Add to Invoice

Click on  Search

Type in "40" which corresponds to the invoice of Nathalie

And click on Search

Select Nathalie's reservation

Click here to add Mario's room to Nathalie's reservation

And click OK.This is how you can transfer articles from an invoice to another