I noticed that you're having trouble finding the customer field when editing your expenses. The reason for this could be that you haven't turned on the billable expense option.
This feature allows you to easily record and track billable expenses, which can be reimbursed by your customer when they receive their invoice. It's important to note that this feature is only available for QuickBooks Online (QBO) Plus and Advanced users. If you're not subscribed to either of these plans, you might want to consider upgrading.
Here are the steps to turn on billable expense tracking:
1. Go to the Gear icon and select Account and Settings.
2. Open the Expenses tab.
3. Click on the Edit or pencil icon in the Bills and expenses section.