If you don’t say you may not know, many European countries such as the United Kingdom, the Netherlands, Germany and other places use public toilets to pay, even if you enter a fast food restaurant or shopping mall, usually an employee sitting at the door to collect money.
This is because Western culture believes that this is a kind of service, and the toilet supplies should be regularly maintained, repaired and cleaned, just as if you hired a person to clean the home, the same reason.
So when you travel, don’t forget to bring more change, otherwise the toilet can only be used.