Email Validation for Laravel does not work

I created a registration page for my users but the email validation is not working, I cant display the alert that the email is already in use. What should I change with my code

Controller code

public function registerUser(Request $request)
{
   
 
    // Validate form input
    $validator = Validator::make($request->all(), [
        'first_name' => 'required',
        'middle_name' => 'required',
        'last_name' => 'required',
        'birthdate' => 'required',
        'email' => 'required|email|unique:user_models,email',
        'password' => 'required|min:5|max:20'
    ], [
        'first_name.required' => 'First name field is required',
        'middle_name.required' => 'Middle name field is required',
        'last_name.required' => 'Last name field is required',
        'birthdate.required' => 'Birthdate field is required',
        'email.required' => 'Email field is required',
        'email.email' => 'Email field should be a valid email',
        'email.unique' => 'The email has already been taken',
        'password.required' => 'Password field is required',
        'password.min' => 'Password should be at least 5 characters',
        'password.max' => 'Password should be at most 20 characters',
    ]);
    
    if ($validator->fails()) {
        // Return validation error if input is invalid
        return response()->json([
            'status' => 400,
            'errors' => $validator->messages(),
            'message' => 'Please fix the following errors:',
        ])->withErrors($validator)->with('error', 'Please fix the following errors:');
    } 
     else {
        // Create new user model and save to database
        $user = new UserModel();
        $user->first_name = Str::ucfirst($request->input('first_name'));
        $user->middle_name = Str::ucfirst($request->input('middle_name'));
        $user->last_name = Str::ucfirst($request->input('last_name'));
        $user->ip_address = $request->ip('ip_address');
        $user->birthdate = $request->input('birthdate');
        $user->email = Str::lower($request->input('email'));
        $user->account_status = '1';
        $user->password = Hash::driver('whirlpool')->make($request->password);
        $user->save();

        $seq_id =  $user->seq_id;
        $user->application_code ="AUP-M231-" . str_pad($seq_id, 6, '0', STR_PAD_LEFT);
        $user->save();

        // Create new ApplicantPPCModel and save to database
        $user2 = new ApplicantPPCModel();
        $user2->email = Str::lower($request->input('email'));
        $user2->pc = $request->input('password');
        $user2->seq_id = $user->seq_id;
        $user2->save();

        // Send activation email to user
        $data = [
            'title' => 'Welcome to Lorem Ipsum University',
            'body' => 'Thank you for registering with us',
            'activation_code' => $user->application_code,
            'first_name' => $user->first_name
        ];
      
        try {
            Mail::to($user->email)->send(new MailNotify($data));
        } catch (Swift_TransportException $e) {
            // Return error response if email fails to send
            return response()->json(['message' => 'Sorry! Please try again later'], 500);
        }

        // Return success response
        return response()->json([
            'status' => 200,
            'message' => 'You have registered successfuly',
        ]);
    }
  

}

Ajax Code

        $.ajax({
        type: "POST",
        url: "/register-user",
        data: data,
        dataType: "json",
        success: function (response) { 
            if(response.status == 400) {
                Swal.fire({
            type: 'error',
            title: 'Oops...',
            text: 'That email is in use already. Please try another one',
        })
                }else {
                    $('.alert-success').removeClass('hideme');
                    setTimeout(function() {
                    $('.alert-success').fadeOut();
                    }, 3000);
                    $('#reg_first_name').val('');
                    $('#reg_middle_name').val('');
                    $('#reg_last_name').val('');
                    $('#reg_email').val('');
                    $('#birth_date').val('');
                    $('#reg_email_confirm').val('');
                    $('#reg_password').val('');
                    $('#reg_password_confirm').val('');
                    $('#reg_id_number').val('');
                    $( "#checkbox-signup" ).prop( "checked", false );
                    $( "#btn-register" ).prop( 'disabled', true );
                    Swal.fire("You're Registered!", "Please check your email before proceeding to the Login Page", "success")
                  
                }
        }
        }); 

Network message
"message": "SQLSTATE[23505]: Unique violation: 7 ERROR: duplicate key value violates unique constraint "the_email"nDETAIL: Key (email)=([email protected]) already exists.

I can display the sweet alert when a user registers successfully but i cant display any error message that will alert the user with the registration.