can i charge a customer for the mileage i travel on their behalf

Yes, you can charge a customer for the mileage you’ve traveled on their behalf, Deejayf1.

The billable expenses feature is exclusively offered in the Plus and Advanced versions of QuickBooks Online. If you’re utilizing a different version, you may need to consider upgrading your account to access this functionality.

Whenever you’re ready, follow the steps below to enable billable expenses in your settings:

1. Navigate to the Gear icon and select Account and Settings.
2. On the Expenses tab, click on Edit from the Bills and Expenses section.
3. Then, enable the following:
4.  
   • Show Items table on expense and purchase forms.
   • Track expenses and items by customer.
   • Make expenses and items billable.
5. (Optional) Turn on the following:
6.  
   • Markup rate
   • Billable expense tracking
   • Sales tax charge
7. Bill payment terms.
8. Then, click Save.

Once done, enter a billable expense to add the customer’s charge on invoices. To do this:

1. Go to +Create and select a transaction, either Bill, Expense, or Check.
2. Select the payee.
3. In the Category column, choose the expense account for the transaction.
4. Enter the description and amount of the expense, then enable the Billable checkbox.
5. From the Customer column, select the customer you want to bill for this expense.
6. You can opt to enter a markup % value, then select the Tax checkbox or choose a tax agency if you want to charge tax.
7. Review all details. Then, click Save and close.

To add this charge to a customer, create an invoice and apply the billable expenses. I've included a screen for reference.

For any additional queries, you can reply anytime in this thread.