Where to add "add_note"?

I have the paypal button plugin and below is the shortcode

[paypal_button type="buynow" name="item 1" amount="30"]
I tried

[paypal_button type="buynow" name="Sales Pitch" amount="30" add_note]
and

[paypal_button type="buynow" name="Sales Pitch" amount="30"] [add_note]

to try and get the note on the checkout page but its not showing up.

I hope its an easy fix could someone help me out with this one. Thanks