There is no minimum scale, because those who start are working for companies which organize it. Try searching on youtube: beermoney phone farm They run 3rd par

There is no minimum scale, because those who start are working for companies which organize it. Try searching on youtube: beermoney phone farm They run 3rd party apps on their phones which automate whole process and they get some percent of profit. I imagine that when they grow they can start working for themselves.