Thanks for posting in the Community, @warren6. 

You can set up invoice terms and turn on the discount feature in the program. This way, you can capture a settlement discount for early payment of an invoiced amount. I'll guide you how.

1. Go to the Settings (Gear) icon at the upper right.
2. Select Account and Settings.
3. Go to Sales from the left menu.
4. Choose Sales form content. 
5. Select your Preferred invoice terms. 
6. Check the Discount box. 
7. Click Save.
8. Hit Done.

The screenshot below shows you the last six steps. 

Once done, apply the discount to your customer's invoice or sales receipt. Here's how: 

1. Go to the + New button from the left menu. 
2. Select Invoice or Sales receipt under Customers. 
3. Choose the Customer. 
4. Verify the Terms. 
5. Add the product and amount. 
6. Select either Discount percentage or Discount value.
7. Enter the amount you want to discount in the Discount field.
8. Click Save.

See the screenshot below to show you the last six steps. For detailed instructions, check out this article: Add A Discount To An Invoice or Sales Receipt. 

After that, please record the early payment of your customer. Just go to the + New button from the left menu and choose Receive Payment. To learn more about this process, visit this article: Record Invoice Payments. 

I'll be right here to help if you need further assistance. Have a great day, @warren6.