Please download:
Android:
https://play.google.com/store/apps/details?id=com.worldcitytrail.app
iOS :
https://apps.apple.com/us/app/world-city-trail/id1627220764
Attention! If you are connected to a hotel wi-fi network, just use it to download the app and then switch to your data for the login procedure. Hotel wi-fi networks are very often unstable, even if they seem to have a strong signal.