Once an Avatax tax code is used in a transaction, it can no longer be changed in the transaction because it is locked to the tax code since there is a document on the admin console reflecting the transaction. To further explain:
1. When a transaction is first created using Avatax Tax Item, Avatax computes the tax, sets the special field provided by NetSuite to avoid tax field being overidden by NetSuite. NetSuite's logic ignores NetSuite's computed tax and uses Avatax's computed tax if
this special field is set.
2. Now if the user changes the Tax Item from Avatax Tax Item to 'Non Avatax Item', in this case 'Non Taxable' or 'Exempt', Avalara does not calculate the tax and also does not blank out the special hidden field so that NetSuites Tax Engine can take over.
If this special hidden field is not blanked out by Avatax, NetSuite ends up using the value in this field and to the end user it appears that tax did not change.
The two options would be:
1. To cancel/close/offset the transaction and create a new one using a non-Avatax tax code.
2. Turn Avatax off, edit the transaction to change the tax code and turn Avatax back on.
Note: If there are many instances like this - where you need to change a tax code from Avatax to non-Avatax, the workaround you may want to consider is to create a User Event script that on Edit will set the taxamountoverride field to null if tax item is not Avatax. If you want this, you can review with your developers to create that script.