Hi there, @jeff15.

You can edit the invoice and add the agreed $60 discount to properly record the $5940 payment in your QuickBooks Online (QBO) account. Let me guide you through the process.

You have two options to add a discount to the invoice. Firstly, let's turn on the discount settings in QBO. Here's how:

1. Click the Gear icon, then select Account and Settings.
2. Select Sales from the left menu.
3. Go to the Sales form content section and click the pencil icon to edit.
4. Turn on the Discount setting.
5. Select Save, then Done.

Once done, you can add the $60 discount to the subtotal on your sales forms as your first option. To do so, you can follow the steps below: 

1. Find and open the invoice transaction.
2. In the Discount value field, enter the $60 discount.
3. Click Save and close.

For your second option, you can add a discount as a line item on your invoice. If you haven't yet, let's first create a service item for the discount. Here's how:

1. Click the Gear icon, then select Products and Services.
2. Select New and choose Service.
3. Enter Discount in the Name field.
4. In the Sales price/rate field, enter the discount as a negative amount (-$60). Keep in mind, this is a dollar amount and not a percentage.
5. From the Income account drop-down, choose Discounts given.
6. Choose Nontaxable from the Sales tax category drop-down
7. Click Save and close.

After creating the item, you can now add the discount item to your invoice. Let me guide you how.

1. Find and open the invoice.
2. Add the discount item you just created in the Product/Service column. You can adjust the discount if you need to, just make sure it's a negative amount.
3. Click Save.

I'm adding this article for more guidance: Add a discount to an invoice or sales receipt in QuickBooks Online.

Just in case you want to set payment terms in QBO so you can give a discount to your customer depending on your agreement, feel free to check out this article: How to Adjust Invoice Payment Terms in QuickBooks Online.

Come back to this post if you have other concerns or follow-up questions about this. I'll be around to provide further assistance.