We appreciate you posting here in the Community, @Forest.

Let me share some insights about your problem with why your sales tax is incorrect and why it is in a line item.

When you migrate from QuickBooks Desktop to QuickBooks Online (US only), there is a limitation on the sales tax payments. The problem is that the payments made in QuickBooks Desktop are applied to the wrong filings in QuickBooks Online companies. As a workaround, customers can delete the migrated sales tax payments and then recreate them in the sales tax center of QuickBooks Online.

For a more detailed explanation of this, you can check this article:

Learn how features and data move from QuickBooks Desktop to QuickBooks Online.

I am here to assist you with any sales tax-related help. Please feel free to comment back if you need my help.