-Not Taxable- is a native NetSuite tax code that some users assign to customers they do not want to make Taxable. There are usage implications for using the -Not Taxable- tax code in conjunction with Avatax.
The -Not Taxable- tax code native tax code within NetSuite will trigger tax calculation if Avatax is enabled.
This is a NetSuite design constraint. Users will want to change the tax code to something OTHER than any of the Various AVATAX tax items or -Not Taxable- to prevent tax calculation from occurring.
*NOTE this is not recommended for users who are also using the Avatax Returns service to file their sales tax returns as can cause incorrect reporting of total sales amounts.