I've got steps to ensure you can create a credit memo for a billable expense, @k-handler.

You'll have to simply create a credit memo by selecting the item manually, and then apply it to the invoice associated with a billable expense. 

First, create a credit memo. Here's how:

1. Click the +New icon, and then choose Credit Memo under the Customers section.
2. Enter all the info needed such as the customer name, the item, etc.
3. Select Save and Close once done.

Once done, apply the amount to the created invoice. You can do it either manually or using the auto-apply credits feature. To do it manually, here are the steps how:

1. Click + New, and then select Receive payment.
2. Enter the customer’s name, and then fill out the required fields.
3. In the Credits section, choose the credit memo from Step 1. Then, in the Payments column, enter how much credit your customer wants to use.
4. Hit Save and close.
   
   

On the other hand, you can turn on the Automatically apply credits option in the Account and settings page to auto-apply these credits to a newly created invoice. Below are the steps how:

1. Go to Settings ⚙, and then select Account and Settings.
2. Choose the Advanced tab, and then tap Edit ✎ in the Automation section.
3. Pick Automatically apply credits.
4. Hit Save, and then Done.
   
   

For more details, please check out this resource: How to create and apply credit memos.

You'll also want to customize your invoices and reports to personalize their info and formats.

Feel free to get back here in the Community if you've got more QuickBooks concerns. Take care and have a nice day.