Hi Luca,
The rain sensor works by delaying the controller using it’s own analog method and the delay is a function of the drying speed of the material used inside the rain sensor. Basically, they are supposed to dictate the “how long to stay off after rain”.
The app can start a rain delay manually, using “Change Rain Delay” from the main menu however this is unrelated to the rain sensor you have installed.
Thanks,
Samer