What do I do with a balance if a customer has gone bankrupt and cannot pay.

Thank you for reaching out to the Community. Let me help you sort this out, @beerandgasman45. 

We can write off bad debt in QuickBooks Online for the customer owes you money but you can't collect it. Please follow the steps below:  

Step 1: Check your aging accounts receivable 

Review other invoices or receivables that should be considered as bad debt using the Accounts Receivable Ageing Detail report:

1. Go to the Reports menu.
2. Find and open an Accounts Receivable Ageing Detail report.
3. Check which outstanding accounts receivable should be written off. 

Step 2: Create a bad debts expense account:

1. Go to Gear icon ⚙ and select Chart of Accounts.
2. At the upper right, tap New to create a new account.
3. From the Account Type ▼ drop-down menu, select Expenses.
4. From the Detail Type ▼ drop-down, hit Bad debts.
5. In the Name field, enter “Bad debts.”
6. Press Save and Close.

Step 3: Create a bad debt item:

1. Go to Gear icon ⚙ and select Products and Services.
2. At the upper right, select New, and then Non-stock.
3. In the Name field, enter “Bad debts.”
4. From the Income account ▼ drop-down, select Bad debts.
5. Select Save and Close.

Step 4: Create a credit note for the bad debt:

1. Click + New.
2. Select Credit note or Give credit.
3. Tap the customer from the Customer ▼ drop-down.
4. In the Product/Service section, hit Bad debts.
5. From the amount column, enter the amount you want to write off.
6. In the Message displayed on the statement box, enter “Bad Debt.”
7. Choose Save and Close.

Step 5: Apply the credit note to the invoice:

1. Select + New.
2. Under Customers, select Receive payment or Receive invoice payment.
3. From the Customer ▼ drop-down, tap the appropriate customer.
4. From the Outstanding Transactions section, press the invoice.
5. From the Credits section, select the credit note.
6. Click Save and Close.

The uncollectible receivable now appears on your Profit and Loss report under the Bad Debts expense account.

Step 6: Run a bad debts report

You can run an Account QuickReport to check all the receivables you tagged as bad debt. To do this:

1. Go to the Gear icon ⚙.
2. Select Chart of Accounts.
3. In the Action column of the bad debts account, click Run report. 

I'm also including this article for additional insights about Bad debt: Write off bad debt in QuickBooks Online. 

Get back to me if you have follow up questions. I'm always here to help. Have a great day!