Can I add billable charges to an existing invoice that has not been sent when charges are not displayed to click and add? ?

I can show you how to add billable charges to your customer's invoice, glenda.corner.

When you want to make your expense be billable to your customers, ensure that you check the Billable box and then enter the customer's name. Then, to add them to your existing invoices, you can follow these steps: 

1. Open the invoice.
2. At the upper-right of the invoice page, click the small left arrow to open the left sidebar. 
3. All billable expenses will list there and just click Add. 
4. Review the updated invoice and click Save and close.

You can do the same steps every time you need to add billable expenses. For more information on how billable expense works and in handling your transactions, check out the articles below: 

• Enter billable expenses
• Common custom reports in QuickBooks Online

Just let me know if there's anything else that you need help with handling customer transactions. Take care and have a great day!