What do I have to do if my daily limit of free internet use has expired?

In the Central Library members of the OBA have access to the internet on library computers for a period of three hours a day. In the branches members have access for 30 minutes a day.
If you would like to have access to the internet for longer, you
can buy a voucher at the point-of-sale terminal. The charge is € 1,- per
30 minutes and there is no further limit to the amount of time you can
use the internet.
The use of the internet and the wifi network facilities is
calculated in units of 30 minutes. If you use less than 30 minutes you
will still be charged for the full period of 30 minutes.