ASYNC VALIDATION — Email Existence Check or other field you can add

asyncValidation.js

import api from "./api"; // your axios instance

export const checkEmailExists = async (email) => {
  try {
    const res = await api.post("/auth/check-email", { email });
    return res.data.exists; // true / false
  } catch (e) {
    return false;
  }
};

// zod message
import { z } from "zod";
import { checkEmailExists } from "../services/validatorService";

export const UserSchema = z.object({
  fullName: z.string().min(2, "Name is too short"),
  email: z
    .string()
    .email("Invalid email")
    .refine(
      async (val) => {
        const exists = await checkEmailExists(val);
        return !exists; // return false for error
      },
      {
        message: "Email already exists",
      }
    ),
  password: z.string().min(6, "Password too short"),
});