Welcome to the Community, Willis. I'd be glad to help you apply partial payments to your invoices in QuickBooks Desktop (QBDT).

Here's how:

1. Open QuickBooks Desktop and navigate to Customer.
   
2. Go to Receive Payments.
   
   
3. Choose a customer in the Received from tab.
4. Locate the invoice for which you want to apply a partial payment and put a checkmark.
5. In the Payment section, enter the partial payment amount.
6. Once done, click Save & Close.
   
   

If the remaining balance becomes uncollectible, meaning you cannot collect money from a customer, you will need to record it as a bad debt and write it off. Let me guide you through the process.

Step 1: Add an expense account to track the bad debt.

1. Go to the Lists menu and select Chart of Accounts.
2. Select the Account menu and then New.
3. Select Expense, then Continue.
4. Enter an Account Name, for example, Bad Debt.
5. Select Save and Close.

You can check out this article for Step 2 on how to close out the unpaid invoices: Write off bad debt in QuickBooks Desktop.

Moreover, you can explore this article for future use when reconciling your account: Reconcile in QuickBooks Desktop.

Keep us posted if you have other concerns or questions about applying partial payments to invoices in QuickBooks Desktop (QBDT). The whole community is here to lend a hand.