Create credit tax invoice in admin console
1) Login to the admin-console and go to the transactions tab.
2) Click new.
3) Fill out origin and destination addresses by clicking the blue hyperlinks for each address (located in top third of the page). Fields with an * are required. These include doc code, customer vendor code, and document date. Tax override data is required only if a tax override is being used.
4) On the lines tab, click add new line. Line No, Quantity, and Amount, are the only required fields.
5) On the first line use positive quantity 1 and the pretax amount of the line. In the tax code field, use NT (non-taxable) Save.
6) On line two, use positive quantity and negative line amount. Save.
Click calculate tax on the left hand side of the page. The positive and negative line amounts cancel out, leaving only the negative tax. The end result is a zero pretax amount (and therefore no impact to total sales) and negative tax only.