how do i find the correct stake to bet?

Hello. I am using RB for 1 day and i am loosing many money. I am always betting the same stake which i think is maybe wrong.

What is the correct stake to bet each time, and how do i find out? The RB always suggest 0 to bet.

I am doing something wrong for sure.

Kelly=30%
min max 4-20
odds 1.60-3.30
adjust for open bets.

where is the wrong spot?