Associating expenses to a specific customer is a great way to gain insights about how profitable your sales are. The ability to seamlessly link expenses to a customer or project is part of QuickBooks Online Plus' billable expenses feature. This allows you to assign a customer each line of an expense. For Essentials, track those expenses to a customer by selecting them in the Payee field. Those expenses would not be tracked to a supplier, so I do not recommend this approach if this is important to you.
The best way to manage your expenses per customer would be by upgrading to Plus to gain access to billable expenses, which includes the "customer" field for expense transactions. You can quickly upgrade your subscription in just 5 simple steps:
Click on the Gear icon and select Account and Settings.
Select the Billing & Subscription menu.
In the QuickBooks Online section, select Upgrade.
Choose the plan you want, and select Upgrade.
Confirm your payment information and select Save.
Once you've upgraded, you can activate the function with the following simple steps:
Go to the Gear icon, then select Account and Settings.