Thanks for being detailed about your concern, @billing87. I'm here to ensure you can match the deposit with a payment and a refund in QuickBooks.

Before we begin, let's first ensure that the payment ($4,000) of Customer A is deposited to the Undeposited Funds account. Here's how:

1. Sign in to your QuickBooks Online (QBO) account and select the +New button.
2. Choose Receive Payment.
3. From the Deposit to field, select Undeposited Funds.
4. Click Customer A on the Customer drop-down and check the invoice ($4,000) in the Outstanding Transactions section.
5. Then, click Save and close.

Next, create a bank deposit and add the refund for Customer B. Let me guide you how:

1. Go to the +New option and select Bank Deposit.
2. Choose the account where you want to deposit the payment in the Account drop-down.
3. Under the Select the payments included in this deposit section, mark the payment ($4,000) from Customer A.
4. Next, add the refund for Customer B in the Add funds to this deposit field.
5. Choose Customer B, in the Received From column.
6. Then, select income account or Accounts Receivable in the Account field.
7. From the Amount column, enter negative 500 (-$500).

After that, the total amount will be $3,500. Once done, you can now match the transactions on the Banking page. 

In QBO, it's easy to get a list of your customers’ outstanding balances to determine how much is still due and how long they’re past due are. You simply need to run the accounts receivable aging report to have this data. 

If you need additional assistance matching the deposit with a payment and a refund, feel free to get back here. I want to ensure your success. Have a good one.