Erik Hanussen added his pseudonym in 1923 in New York, in the movie it happened in Germany in 1919.
Erik Jan Hanussen was killed in the SA Prison Papestraße in Berlin, not in the woods, like in the movie. It also happened after the burning of the Reichstag, not before that as in the movie.
Erik Jan Hanussen started performing as a hypnotist before WW1, while in the movie it was discovered only after the war.
Erik Jan Hanussen was born on the 2nd of June, not on the 20th April, as suggested in the movie.