AP invoice import tax data on nontax line error

Summary:

I am importing an interproject Payables invoice. The AP invoice is generated from the corresponding AR invoice. The AR (and thus the AP) invoice has a tax code calculating a zero tax amount. When I import the interproject AP invoice I receive the rejection reason Tax data found on nontax lines. But the tx rate in the AP invoice line is correct. What causes the AP invoice line to be determined as being non taxable? And how to avoid this going forward as we intend to use both interproject billing and intercompany billing.

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