How to create custom validate with Meteor.method (server)?

help
1

I would to create custom validate that call method from server

// use simple:­reactive-method (server directory)
Meteor.methods({
   myValidate: function(opt){
      if(opt == 'A'){
         return true;
      }
      return false;
   }
})

// schema (both directory)
SimpleSchema.messages({
    "nameMsg": "[label] must be A"
});
.......
name: {
        type: String,
        max: 250,
        custom: function () {
                var nameExist = ReactiveMethod.call("myValidate", this.value);
                if (nameExist) {
                    return "nameMsg";
                }
            }
        }
    }

Please help me.