danmanuele, good afternoon.
The IF function syntax is missing what to do when the clause is False.
A parenthesis is also missing by closing the first range.
=IF(G23=0, P15/Sum(D11:F11), IF(G23>0, P15/Sum(D11:G11) , What to do here when FALSE?)))
I hope it helps.
Belo Horizonte, Brasil.
So your second if doesn't say what to do if false, so it displays false!
IF(G23>0,P15/Sum(D11:G11),"HERE IS SOMETHING ELSE!")