Hello there, @JBVan. I'm here to share some details about the error you received when merging accounts in QuickBooks Online (QBO).
The error you received occurs when you're trying to merge a default account. These are accounts automatically created by the program after you set up your company. To know more details about this, feel free to check this article: Accounts that can be edited, but not deactivated or merged.
As a workaround, you can create a journal entry to move the data from the account you're having a problem to the correct one. Before performing the process, I highly recommend reaching out to your accountant for guidance to make sure your transactions are accurate and well accounted for.
I've also attached this helpful resource that you can access at any time to look for references and guides in navigating your QBO: Learn about QuickBooks Online with how-to videos.
If you have any other concerns about merging accounts in QBO, please don't hesitate to get back here again. I'm just around the corner to help. Take care and have a good one.
