The Tax Element for Stripe is a separate plugin (which you can find in your subscription download area).

Install the Stripe Tax Element for RSForm plugin as you would install any other Joomla plugin. Be sure it's enabled in your Plugin Manager once installed.

Note the plugin ordering is important with this element and needs to be after the System - RSForm! Pro Payment plugin. To change plugin ordering you can click the Order column, then drag and drop the plugins in the order you want them to load. Find the System - Taxes for RSForm plugin and drag it to the bottom of the System plugins. It may be easier if you extend the search filters to only show Enabled System plugins.

Now you can go to the form you wish to insert the tax element. Find the Stripe Tax element and add it to your form.

You can leave the caption and description fields blank so the element is hidden.

In the Attributes tab, you can set your sales tax and/or fee percentage (i.e. 20%), or fixed value (i.e. 2.00).

We recommend adding a Free Text element somewhere on your form that explains how much in taxes or fees are being added so your users aren't confused when the total is different from what they seen on the form.

The ordering of this element within the form is important. It must be below all of the other Payment Elements, otherwise it won't add taxes to the total that is passed to the Stripe gateway.