Isometric Screen To world point with fixed y axes

Hi. Thank you for the help. I am trying to place a cube using Camera.main.screenToWroldPoint on the mouse or touch position.

The results appear correct in the game view, but my game Object is moving on the X, Y and Z. I need a way to fix the Y position at y = 1 and have the X and Z position translate correctly for the Game View.

I am using an Orthographic Camera at 30,45,0 rotation for isometric view. I'm guessing there is an easer way than working out the math?

Thank you.