You can enable the invoice number displaying under WooCommerce > PDF Invoices > Documents > Invoice > Display invoice number, selecting the Invoice Number option:
Really sorry this setting escaped me… Sorry to have disturbed you so little.
Thank’s you !
You don’t have to apologize at all: We are always ready to help you!
Actually, we are aware that we have many options and that there is always the possibility that you might overlook some of them 🙂
Do not hesitate to write whenever you need anything else! 😉