Hi, Carrie. There are two methods you can use to classify your expenses by customer. You can either use the Expenses tab to view transactions by customer or running a report to classify and analyze them. I'd be glad to assist you through the steps.

If you meant filtering the expense transactions to show only those associated with a specific customer from the Expenses tab, follow these steps:

1. Log in to your QBO account.
2. Click on Expenses in the left menu.
3. Under the Expenses tab, click on the Filter button.
4. In the filter options, click the Payee dropdown.
5. Select the customer whose expenses you want to view.
6. Click Apply.

On the other hand, if you need a report that displays the expense transactions categorized by specific customers, follow these steps:

1. Go to Reports in the left menu.
2. In the search bar, type and select Transaction List by Customer Report.
3. Once the report is opened, click on the Filter button.
4. Filter your data by adding a filter tab for the Customer you want to see the expenses for.
5. Click Equals, and then the specific customer name.
6. Click add another filter for the Transaction Type.
7. Select equals and then Expense.
8. Click Run report.
9. Once everything is okay, click Save.

Additionally, if you'd like to bill your customers for an expense in the future, you can refer to this helpful article: Enter billable expenses in QuickBooks Online

Lastly, I'm pleased to inform you that you can elevate your financial management with the help of our QuickBooks Live Expert Assisted team. They specialize in helping you transform your financial management and provide personalized advice for your business's specific demands. Feel free to check them out anytime.

If you have any more questions or need further assistance with expenses, please don’t hesitate to ask through the thread. We’re always here to help you make the most out of QuickBooks.