When you go to the booking form, you are shown no tickets, because to book subscription prepaid tickets and post paid, you need a promotional CODE
You will get your code by email after purchasing a subscription.
In the email you will get a link which makes everything more simple!
Regulars may also get a FREE code for postpaid tickets.
As you can see in the image below in red, you need to:
You may also book from your Android and Iphone!
Here is a preview of the form: