Use custom field to change tax rate

I’m trying to set up a checkbox in the cart which - when checked - changes the tax rate of eligible products to 0. I struggle to make that happen though. Here’s my setup:

I setup (and enabled) the Custom Fields module like this:

And created a new Tax Group with these rules:

Then I created a checkbox field solar within the cart:

<form method="post" action="{{ current_url }}">
  <input type="hidden" name="update_cart" value="1">

  <div class="form-check">
    <input name="solar" class="form-check-input" type="checkbox" value="1" id="solarCheck">
    <label class="form-check-label" for="solarCheck">No taxes!</label>
  <button type="submit">Submit</button>

But when I submit that, there is no tax rate change at the product in the cart (which has the newly created Tax Group assigned). What am I missing?

Anyone has any ideas on this?

Try using in your tax rule conditions to indicate you want Commerce to check the value of that custom order field.