How to setup and post Customer Early Payment Discounts in Quickbooks Desktop Pro 2019? Nothing shows up in Customer Payment under Discounts Applied Box at bottom page?

It's good to have you here, @KClulee.

Tracking sales discount should show up on your expense account and not on an income. You can choose any expense account when receiving an early payment from your customer. Let me guide you in setting up an early payment discount in QuickBooks.

1. Go to the Customers menu.
2. Choose Customer Center.
3. Click on the customer's name to look at their Transaction List.
4. Open the Invoice and press on Receive Payments button in the header.
5. Once the Customer Payment window is opened, select the Discounts And Credits button
6. Click the Discounts and Credits tab.
7. Select an expense account to track your Discount Account. 
8. Click Save & Close. 

You can read through these articles to learn more about tracking your income and expense transactions:

• Accounts Receivable workflow

• Accounts Payable workflows

• Customize customer, job, and sales reports

Also, I'd suggest consulting with an accountant so you'd be assisted properly in tracking your sales transactions.

It'll be always my pleasure to help if you have any other questions. Just leave it in the comment section down below.