Couldn't access the main building door despite downloading the Nuki app & following host's instructions. Code for the main door was invalid. Contacted host in Airbnb app & the 'emergency number' given (... 8888) but no response despite informing the host in advance of our check in time. Contacted Airbnb support. Found another number, one Billy - who claimed to be one of the hosts - answered. Billy admitted he was in Asia! After almost two hours struggling to get in, a tenant of the building let us in. We went to the apartment & found out the app only worked for the apartment door & not the building door. Informed Billy. Then only Billy informed us there's actually a physical key to the main door in case the app didn't work. By that time we were already heading to a hotel. Nobody in their right mind wants to stay in an apartment where they can't access the building. Request for refund has been met by total silence from the host despite giving all evidence.