Hello Info1859,
Welcome to the Community page,
You could enter it in on the other box in the customers details section as there is not option for customer id in Quickbooks however this will just show in there and nowhere else. Or you could create a custom field box and enter it in there each time manually on the invoice, if you need to see it on the invoice. Otherwise there is no other way to do it in QuickBooks, you can leave this as feedback within the main cog wheel.
