I am creating a Registration API using DRF but I am getting an custom error message like “Custom user with this email already exists”

Please reivew the code below

View.py

from rest_framework import generics
from rest_framework import status
from rest_framework.permissions import AllowAny
from .serializers import RegisterSerializer
from projectname.utils import custom_response

class RegisterView(generics.CreateAPIView):
    serializer_class = RegisterSerializer
    permission_classes = [AllowAny]

    def create(self, request, *args, **kwargs):
        serializer = self.get_serializer(data=request.data)
        if serializer.is_valid():
            user = serializer.save()
            response_data = {
                "username": user.username,
                "first_name": user.first_name,
                "last_name": user.last_name,
                "email": user.email,
                "user_type": user.user_type,
            }
            return custom_response(
                success=True,
                message="User registered successfully",
                data=response_data,
                status_code=status.HTTP_201_CREATED
            )
        else:
            return custom_response(
                success=False,
                message="User registration failed",
                errors={"error_message": list(serializer.errors.values())},
                status_code=status.HTTP_400_BAD_REQUEST
            )

serializer.py

from rest_framework import serializers
from .models import CustomUser

class RegisterSerializer(serializers.ModelSerializer):
    password = serializers.CharField(write_only=True)
    
    class Meta:
        model = CustomUser
        fields = ('email', 'username', 'first_name', 'last_name', 'user_type', 'password')

    def validate(self, data):
        required_fields = ['email', 'username', 'first_name', 'last_name', 'user_type', 'password']
        errors = {}

        for field in required_fields:
            if field not in data or not data[field].strip():
                errors[field] = f"{field.replace('_', ' ').capitalize()} is required."

        if CustomUser.objects.filter(email=data.get('email', '')).exists():
            errors['error_message'] = "Email already exists."

        if CustomUser.objects.filter(username=data.get('username', '')).exists():
            errors['error_message'] = "Username already exists."

        if errors:
            raise serializers.ValidationError({"error_message": list(errors.values())})

        return data

    def create(self, validated_data):
        user = CustomUser.objects.create_user(
            email=validated_data['email'],
            username=validated_data['username'],
            first_name=validated_data['first_name'],
            last_name=validated_data['last_name'],
            user_type=validated_data['user_type'],
            password=validated_data['password']
        )
        return user

models.py

from django.contrib.auth.models import AbstractBaseUser, BaseUserManager, PermissionsMixin
from django.db import models

class CustomUserManager(BaseUserManager):
    def create_user(self, email, username, first_name, last_name, user_type, password=None):
        if not email:
            raise ValueError('The Email field must be set')
        email = self.normalize_email(email)
        user = self.model(email=email, username=username, first_name=first_name, last_name=last_name, user_type=user_type)
        user.set_password(password)
        user.save(using=self._db)
        return user

    def create_superuser(self, email, username, password=None):
        user = self.create_user(email, username, password)
        user.is_admin = True
        user.is_staff = True
        user.is_superuser = True
        user.save(using=self._db)
        return user

class CustomUser(AbstractBaseUser, PermissionsMixin):
    USER_TYPE_CHOICES = (
        ('child', 'Child'),
        ('parent', 'Parent'),
        ('admin', 'Admin'),
    )

    email = models.EmailField(unique=True)
    username = models.CharField(max_length=30, unique=True)
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    user_type = models.CharField(max_length=10, choices=USER_TYPE_CHOICES)
    is_active = models.BooleanField(default=True)
    is_staff = models.BooleanField(default=False)
    is_admin = models.BooleanField(default=False)

    objects = CustomUserManager()

    USERNAME_FIELD = 'email'
    REQUIRED_FIELDS = ['username', 'first_name', 'last_name', 'user_type']

    def __str__(self):
        return self.email

response

{
    "status_code": 400,
    "status": false,
    "message": "User registration failed",
    "data": null,
    "errors": {
        "error_message": [
            [
                "custom user with this email already exists."
            ],
            [
                "custom user with this username already exists."
            ]
        ]
    }
}

here i want to show the respose like

• Email already taken
• username already taken

but i donot know, why i am not geting above error, please let me know the reasone, I will be very thankfull to you