hopefully simple fix to tax problem

hopefully simple fix to tax problem

I am having a problem with my tax and need help to understand the purpose of a field. When I put in an amount or % in the field pointed out in the screenshot, the tax seems to work. When I leave it at zero, it doesnt work. The downside is that when I have an amount in that field it is requirding additional money. How do I keep this at zero, but get the tax to work? What is the purpose of that field?

Thanks so much for your help.

I hope to eventually have this all figured out and working soon. It is taking me waaaaaayyyy too long.

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Aw: hopefully simple fix to tax problem

Ok...I now have it figuring out the tax; however, it is figuring out the tax of the shipping, not the tax on the product.

I still need help. I need to find out what I am missing that it isnt figuring out the tax for the product at checkout.

I have the tax setup for payment. I am just not sure what I am missing. Any help is appreciated.