validateClient:true not preventing calling server function when input on client is invalid

I am using a simple middleware which has validateClient set to true with a server function. I expected when I call server function with invalid input, an exception on client side prevent calling the server function. But seems the validation occurs on the server side. I provided the code in the screenshot attached. Am I missing something? Thanks. ps: in snippet below there is a typo: validate() should be validator()