Need to wire "C" wire to thermostat
It's the terminal between R and W

See the white wire coming from the cable to the A/C compressor? Since the red wire in that cable goes to the Y terminal, the white wire in that cable has only one place it can go for the A/C to work, and that is the C terminal on the control board or its equivalent transformer terminal.

P.S. as to how you have the thermostat hooked up? It's spot on.