How do you add a billable expenses to an previously created open invoice? This was easily done in the old invoice experience but I cant figure out how to do it now.

You can add the billable expenses to your customer's invoices by linking them from the sale transaction, rzinserrm. I can guide you with detailed steps.

In the new sales form layout, you can add the billable expenses created by selecting the Suggested transactions from the existing invoice entry. Let me show you how:

1. In your QuickBooks Online account, go to Sales from the menu panel and select Invoices.
2. From there, find and click on the Edit icon of the existing invoice transaction.
3. Hit on the Manage option and click the Suggestions dropdown.
4. Then, select the Suggested transactions and Add the specific billable expense entry.

Once done, this will link to the open invoice transaction.

Moreover, I've added this reference to help you track and record customer-paid invoices in your file: Record invoice payments in QuickBooks Online.

If anything occurs while managing customer transactions in your account, please leave a reply in the comments below. I'll be around to help.