Billable expenses feature was not available in QuickBooks Self-Employed or QuickBooks Simple Start.
QuickBooks Self-Employed is designed for independent contractors and freelancers and has a more limited set of features compared to other QuickBooks products. QuickBooks Simple Start is a basic accounting software for small businesses and also has a limited set of features.
If you need the billable expenses feature, you may want to consider upgrading to QuickBooks Online Essentials or QuickBooks Online Plus, which offer more advanced accounting and invoicing capabilities. The billable expenses feature is available in these products, and it allows you to track expenses that you incur on behalf of a client and bill them back to the client as a separate line item on an invoice.