How can I generate an invoice for several delivery notes from the same customer?

You can generate an invoice from multiple delivery notes from the same customer if you access Sales > Sales Notes, filter by Customer, and those filter options you need and select the delivery notes/delivery notes you want.

If you want the delivery notes to be sorted by date so that when generating the invoice they are shown in that order, you must click on the Date column and choose the desired order.

Click on More > Generate > Invoice.

An invoice will be generated with all the delivery notes we have selected.