If you're looking to manage your invoicing in Sage 50, adding an invoice number is a must. With the help of this article, you'll be able to do just that. First, open the Invoice window. Next, click on the Options button in the toolbar. This will open the Options dialog box. Sage 50 Invoice Numbering.  From here, select the Add an Invoice Number option. Enter a unique invoice number and click OK. You're now ready to start entering your invoices.If you are using Sage 50 as your invoicing software, then you will want to add an invoice number to each invoice. You can do this in a few different ways. One way is to go to the Settings menu and select Invoice Numbering. Then, enter a unique number for each invoice. Another way is to go to the Tools menu and select Add Invoice Number. This will open the Add New Invoice window. In this window, you can enter a number or name for the invoice.