the Physics.IngoreLayerCollision()-Method is used to disable collision between two layers.
With your code, the Physics engine don’t know which objects should be ignored for collision with layer8.
If you never need collision with layer8 you can just remove the Collider-components from the GameObjects on layer8.
PS - the error you get is because you try to pass inappropriate parameters to the function. So when coding you can type Physics.IngnoreLayerCollision and as soon as you type the bracket there will be anpther popup (tooltip) that shows you all the overloads for this method and its parameters. This can help you to avoid errors like this.