According to my textbook $$\frac{v_o}{i_s} = -R_1\left(1+\frac{R_3}{R_1}+\frac{R_3}{R_2}\right)$$
The current on the terminal branches are both 0 for an ideal op-amp. Using KCL we see R1 and R2 have a current of \$i\$ going to the left of them and R3 has no current on it.
simulate this circuit – Schematic created using CircuitLab
Since this is an ideal op-amp, the voltages at the input terminals are both 0 with respect to the ground. And Vo is the voltage between R1 and R2 because the current through R3 is 0. This means Vo is the output voltage of a voltage divider where Vin is 0. Thus, $$\frac{v_o}{i_s} = 0$$
I have been getting wrong answers when I'm using KCL so I assume I'm somehow not able to apply it correctly but I don't exactly know from where does the error come. Isn't this a valid use of KCL?