Can anybody figureout why validate_email method unable to call in serializer?

I'm using django and djoser for backend authentication and react on frontend side. I want to put a condition on email in serializer that if email already exists send them error msg that "email already taken" otherwise register.

serializer

class UserCreateSerializer(UserCreateSerializer):

    class Meta(UserCreateSerializer.Meta):
        model = User
        fields = ("id","username","email","password")

  def validate_email(self, email):
    if User.objects.filter(email=email).exist():
        msg = "email already taken"
        raise serializers.ValidationError(msg)
    return email

djoser settings in settings.py

DJOSER = {
    ...,
    "SERIALIZERS" : {
        "user_create":"accounts.serializers.UserCreateSerializer",
        "user":"accounts.serializers.UserCreateSerializer",
        "user_delete":"djoser.serializers.UserDeleteSerializer",
    },
}

accounts/models.py

from django.db import models
from django.contrib import auth

# Create your models here.

class User(auth.models.User,auth.models.PermissionsMixin):
    
    def __str__(self):
        return "@{}".format(self.username)

Many many thanks in advance reading and answering this question..