The punishment for not having a ticket is being issued with a standard fare. There is no punishment in the bye laws for not paying the standard fare (read the bye laws yourself).
4. (1) A passenger, on entering a light rail vehicle, who is not in possession of a valid ticket, is liable to pay the standard fare.
(2) A passenger who is on a light rail vehicle without a valid ticket shall pay the standard fare to an authorised person immediately or, at the discretion of the authorised person and where the authorised person is satisfied as to the name and address of the passenger, within a period of 14 days of having so entered the light rail vehicle, to the operator concerned.
(3) An authorised person shall issue the relevant ticket to a passenger who has paid the standard fare and such a ticket entitles the passenger to travel to the next terminus.
(4) Where a passenger is found on a light rail vehicle without a valid ticket by an authorised person and the passenger refuses to pay the standard fare immediately, the authorised person may request the passenger to leave the light rail vehicle at the next stop and the passenger shall comply with such a request.
(5) In this Bye-law “standard fare” means a fare of €45.