Hey there SML709,
Welcome to the QuickBooks Community! Thanks for reaching out to us here. QuickBooks Online is a great tool able to help keep your books balanced. I would be happy to point you in the right direction.
The billable expense on your original invoice, may still be linked. I suggest opening the invoice and remove the checkmark in the 'billable' column, then save. If you experience the same outcome, I recommend reaching out to the support team outside of the Community. They'll be able to view your screen in a secure setting and guide you back to your QuickBooks goals. You can reach them by following one of these methods:
Schedule a Callback or start a Chat: click (?)Help in the upper right > type and enter "Contact support" into the QB Assistant > click Contact Us > explain your situation > click Let's Talk > choose Get a callback or Start a Chat.
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If you have any other questions, feel free to reach out here.