Hey @scott.william, it looks like you reached out to our support team about this, and my colleague Kenyon replied to you. Just wanted to paste their response here for anyone else experiencing the same issue:
The tax code error we're seeing seems to be coming from the '0' we have in the 'Total Tax' field:

We've selected "TAX" as the code, but then we say the tax amount is zero. That doesn't make much sense to me as I'd think we would use "NON" as the tax code if no tax should be supplied. QuickBooks sees this as invalid so we'll need to make sure those values align. I'm not sure what it should be since tax is so nuanced, but you may want to have a closer look.