Avatax: How can you credit an invoice for tax only to an SST state?

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I know what you're thinking -- ask Avalara. I have created multiple cases for this question and they just email me a link to a KB article that tells me how SST states work and don't answer the question. Then they close the case. They will not answer the question.

For non-SST states, we follow the Sage procedure. One line taxable, one line non-taxable using TX and NT respectively. For SST states, as soon as you use an NT line, the whole thing goes to $0.00. You are apparently not supposed to use NT lines when you use AvaTax in SST states.

So I've been just overriding the tax amount in both Sage 100 AND then I have to go into Avatax and manually override it there too. But you're not supposed to do that either with SST states. But I don't know what else to do to make it credit sales tax.

Anyone else use Avatax with Sage 100 and have an answer for me?