This is a very strange place. Firstly, there is no check-in.
The apartment manager will helpfully email you a few hours before you are due to check-in, when you are travelling in a plane/train/car, so you have no idea how to get in. But it's ok, the door is open, and they leave all the room keys in a little box.
Then your apartment manager (Maya, I believe) will lie and tell you there is cleaning. There is no cleaning. Not even toilet rolls.
But the best one is that she will tell you she wants to meet you and will turn up earlier than she says and say she wants to take your passport with her for "an hour" or "a few hours" or "some time" because she needs it in "the office". Not a photocopy, not a photo, but she wants your passport.
This is ridiculous. If you stay here, do not give her your passport! She is trying to register you to pay the city tax, but she does not need your actual passport. No other hotel/apartment does this. They all just pay the tax. Instead of listening to Maya (or indeed the owner, Srdan Petrovic), just go and pay the city tax at the office yourself (it is in the old town and you will be going there at some point, it is very central). It is €1 per person per night
Basically, don't stay here and deal with insane people who have no idea about check-in, registration and who are barely contactable