After reservation we didn't get a reaction on our question about the check in (the advertisement said it was also possible at the appartement).
After calling we didn't fully understand each other and the line was hung up, so we had to travel to central station to get the keys.
I assume from the other reviews they never want to check in at the apartment itself?
After receiving the key everything was fine, the apartment wasn't as clean as I hoped but fulfilled our basic needs.