New Vendor name created in customer list in error. As a result, when I paid their bill, its not showing up in the Vendor Summary of Transactions Report, but instead as a negative number on the Customer Summary of Transactions Report.

Good day, lianeshine. 

Allow me to share some information about managing your transaction in QuickBooks Online (QBO). 

Yes, I would agree that Journal Entry is the last resort when fixing the accounting issue in your company file. To fix this, you'll have to delete the transaction under the customer profile and recreate it. Otherwise, you can make the customer inactive. 

Here's how:

1. Find the transactions you want to delete, and open them one at a time.
2. At the bottom of the page, click More.
3. Choose Delete.
4. Click Yes to confirm the deletion.

To make customer inactive, you can follow the steps below: 

1. Go to ​the Sales menu, then the Customers tab.
2. Select the customer's name to open their profile.
3. Click the dropdown ▼ next to Edit.
4. Choose Make inactive. Then confirm by selecting Yes, make inactive.
    

You can also read this article for more information: Void or Delete an Invoice or Other Transactions.

Please post again here if you have any other concerns about deleting transactions in QuickBooks. I want to ensure you'll be able to do this smoothly. Have a good day ahead.