Post Preview -> Page not found

Hello!

Ever since I created my website (in September) the Preview Post button has not been working. It always said “Page could not be found”. Since I didn’t have so much traffic in the beginning, I didn’t really care. But now I would like to preview my posts before putting them online. How can I do it? How to fix this error?

My site is https://www.studentoftheworld.de

Thanks a lot in advance and best regards

Silke