Level 75
You have to create your own validation rule, where you use joins and check if that email exists in your database.
https://laravel.com/docs/7.x/validation#custom-validation-rules
https://laravel.com/docs/7.x/queries#joins
You can use this joins
use App\User;
Use::select('users.id', 'users.email', 'roles.name as role')
->join('model_has_roles', function ($join) {
$join->on('users.id', '=', 'model_has_roles.model_id')
->where('model_has_roles.model_type', User::class);
})
->join('roles', 'model_has_roles.role_id', '=', 'roles.id')
->get();