I built a website with a quiz, where the quiz itself is basically a html site with a form for the question and the answer-possibilites, where the user can select the answer, compare if it was the right answer and the continue to the next question.
The problem is: after answering some of the questions, some users get a CSRF Verification error 403:
The problem only occures for some of the users (maybe like 5 out of 100) and the confusing thing is that at first they can normally answer some questions, before they get the error. Because the site is basically the same (it just reads in new questions and answers) I can not explain to myself how this error can occur.
Is there some server-side configurations that can be made in order to avoid this? I have no log-in built in the website, I am mainly using sessions and of course the cookie, where the session_id is saved on the user side.
Or is the problem because of the browser configuration of some of the users?