I know a way to write off a specific vendor's negative Accounts Payable in QuickBooks Online (QBO), g_Quik_Online. I'll guide you through the steps to ensure a smooth experience. 

We can use a Wash account when creating vendor credits in QuickBooks Online. This way, the amount won’t reflect in your Accounts Payable account.

Here's how:

1. From the left navigation pane, select the Accounting menu and click Chart of Accounts.
2. On the Chart of Accounts tab, click the New button.
3. Choose a Bank for the Account Type. You can choose any detail type you want for your clearing account.
4. Type in the Name for the clearing account.
5. Click Save and Close.

Next, let's create a Journal Entry (JE) to transfer Receivable to Wash Account:

1. In your QBO account, click on +New, then select Journal entry.
2. Select the Wash Account on the first line, then enter the amount in the Debit column.
3. Select Accounts Receivable on the second line, then put the amount in the Credit column.
4. In the Name column, select your customer.
5. Once ready, click on Save and close.

Furthermore, after you place the amounts into the right accounts, you can then reconcile your account to ensure that every record is correct: Reconcile an account in QuickBooks Online.

Feel free to get back here in the Community if you have further questions about the process. I'll be happy to help. Keep safe!