How do I add billable expenses to a particular invoice?

Hi there, 

Welcome to the QuickBooks Community. The program offers a variety of features that make it easy for you to manage your work. I'll be happy to share more info and point you in the right direction so you can get the resolution you need. 

I encourage you to check out the following article that shows you how to: Enter billable expenses. The article shows you how to add billable payments to invoices on Step 3 in the article. Let me know how you make out as you browse through the article. 

In case you need additional assistance I encourage you to contact our support team so they can assist you further. Here are our contact details: 

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Feel free to keep me posted on how you make out. Enjoy the rest of your day.