This indicates that the exempt tax code mapping is required by your QuickBooks Online locale. To resolve this, simply set a new exempt tax code under the Taxes tab of the QuickBooks Online Configuration and retry the batch.
Please note that different QuickBooks Online country versions require different Tax configurations. If your QuickBooks Online account does not require Tax Exempt, then this message means that the QuickBooks Online Config has lost the Locale, i.e. the country version:
To resolve this, please re-save the configuration, i.e. go to Set Up QuickBooks and the corresponding Config, and click Save. This will re-populate the Locale: