Thanks for joining on this thread, @JAR2020.

It would be my pleasure to walk you through the step-by-step instructions on how to record interest to the overdue accounts without doing separately in QuickBooks Online. 

First, if you haven't created an interest item yet, let's go ahead and create it. 

Here's how:

1. Click the Gear icon, then choose Products and Services.
2. Tap New.
3. Select either Non-inventory or Service.
4. Enter the desired name of the interest.
5. From the Category ▼ dropdown, select the category that fit defines the fee. 
6. Hit Save and close.

Once done, if you haven't sent the invoices yet, you can add the fee as a line item to the existing invoice. Let me guide you how: 

1. Go to Sales, then go to the Customers tab.
2. Choose the customer, then look for the past due invoice.
3. Add the interest item in the unused line, then enter the amount.
4. Tap Save and send or Save and close.

On the other hand, if the invoices are already sent, you'll need to create a new invoice to add the fee to what my colleague mentioned above. 

Here's how: 

1. Click the Plus sign (+) icon, then choose Invoice.
2. Under the PRODUCT/SERVICE column, add the interest item.
3. Enter the amount manually in the AMOUNT tab.
4. Tap Save and send or Save and close.

You also have an option to set up automatic late fees to your invoices. So QuickBooks can apply them automatically. Let's turn on the late fees feature first by going to the Settings, then select Account and Settings. After, choose the Sales tab and turn on the radio button under the Late fees field. 

For more details, browse this article: Set up and apply automatic late fees to invoices. 

You can always access any customer's reports to review the transactions you've made, then customize it to show the specific parts. 

Additionally, I've attached an article about how to personalize sales forms and add the info that implies most to your business. 

• Customize invoices, estimates, and sales receipts in QuickBooks Online

Let me know if you have follow-up questions. I'm glad to assist. Have a great day!