CartThrob: Setting no tax on on-the-fly products

Question

I understand the add to cart form can take a parameter to disable tax on a product like so.. (although the docs seem to indicate it should be 'tax_exempt'?)

{exp:cartthrob:add_to_cart_form on_the_fly="y" no_tax="yes"}

I am using this to create phone orders but sometimes a product may not have tax so I was hoping to add a checkbox, something like this:

<input type="checkbox" name="no_tax" value="yes" />

Unfortunately this does not appear to work for me, just wondering if there are any undocumented features that will do what I want?

Answer 1

The tax_exempt parameter is renamed to NTX and then its value is encrypted by the CartThrob form tag before being added as a hidden input, so it's not quite so simple.

But a little bit of PHP can do this for you (or a you could write a simple plugin if you're averse to PHP in templates).

<input type="checkbox" name="NTX" value="<?php echo ee()->encrypt->encode('yes'); ?>" />

You may or may not need to load the Encryption library first:

ee()->load->library('encrypt');