The cause of this issue is when a customer is trading in a vehicle that is worth more than the vehicle that they are purchasing. Certain taxes, such as the TX Vehicle Inventory Tax, are set to to tax the deducted amount of the trade in. If this value is negative, the final tax will also be negative. On Modal Dashboard, Modal displays all taxes as 'Sales tax'.
Contact Modal support at firstname.lastname@example.org to have this setting turned off. Once this is complete, orders should no longer display a negative tax value when the balance of the trade is negative.
Document Change Log
• 1.0 / October 28, 2020: Initial release