Pro is paid: the monthly price is stated when you order it and is charged repeatedly to the card you entered, at the start of each following month. You can cancel the subscription at any time in your account; Pro then lasts until the end of the paid month and nothing further is charged. If a payment fails we retry it a few times and let you know; if it still does not go through, Pro ends.
The coupon stays free with Pro. The status only decides how many coupons you may take a month once such limits are in place — the numbers are stated at registration and in your account. For every paid month we issue a simplified tax document to your e-mail.
A free month of Pro for two people you brought in who bought is added to the end of your paid period; nothing is charged for it.