First of all turn ON Bluetooth and GPS (location) to be able to scan for and connect to Bluetooth cubes and Mi Band bracelets.
On Android you have to give the app the necessary permissions ("Access location" and "Access storage and photos").
Make sure that the cubes are not connected to any other device or app (like Rubiked or Supercube) before starting CubeSmith.
You can connect the cubes long before you start your performance. Once you start a routine, the connection to the cubes and the Mi Band (if you use the extra feature) will stay alive for a long time, and will be renewed upon disconnecting. When a Giiker cube is connected, it can't be detected on another phone, so noone else can see your cube in the list of available Bluetooth devices.