I paid my trip using contatless payment and now I can see a card pre-authorisation in my online bank. What does this mean? 

When you use contactless payment to pay for your trip some credit or debit cards will be charged a pre-authorisation, which can be around € 1-20. The amount of the pre-authorisation and the schedule for releasing the funds is up to your bank. If you have additional questions on pre-authorisation, we recommend that you to contact your bank.