Hi, synergyaquatech. Thanks for visiting the Community.
Assigning customers to expenses and credits is unavailable in QuickBooks Online Simple Start and Essentials. Consider upgrading to QuickBooks Advanced or Plus to take advantage of this feature.
Once you're all set up and ready, let's enable the Track expenses and items by customer option. Here's how:
- Log in to your QuickBooks company on a web browser.
- Go to the Gear icon and select Account and settings.
- Click the Expenses tab, then hit the Edit button.
- Toggle on the Track expenses and items by customer option.
- Click Save, then Done.

After that, you'll see the Customer column when creating an expense transaction. Here's a visual reference:

Let us know if you have further questions. We're here to help.