This is a tax that is paid to the City of Amsterdam. In 2020, € 1.50 will be charged for every visitor of entertainment on water, on land (round trips) and city tours (with or without vehicle). The prices of the Pancake Boat do not include entertainment tax. You will pay this amount online if you buy your tickets via this website. If you have bought tickets from another provider, you pay the entertainment fee on board with PIN or credit card.
More information about the entertainment tax can be found on the website of the City of Amsterdam.