If you click on "Show Conditions"
"You can cancel (exchange or refund) your ticket before the first day of validity for a fee of 10,00 EUR in exchange for a voucher. Thereafter, cancellations are excluded."
"You can use all trains and IC Bus services indicated on your ticket. You can use any local train (i.e. RE, RB, S). Passengers on train and IC Bus services with mandatory reservation must reserve a seat.
Payment by credit card (may require 3-D Secure Code), Sofort, PayPal and paydirekt possible.
In many cities your ticket is also valid for local public transport, both on the outward and return journeys. Departure and destination points must be within the tariff zone permitted by the City-Ticket. You can find the list of permitted cities by searching for "City-Ticket" on www.bahn.de."