We currently have this error.

The user.10.phone field has a duplicate value

As you notice that this is not a user friendly message and we can update that by:

$rules = [
.... 
];

$customMessages = [
    'bla.distinct' => 'The bla has duplicate custom message here'
];

$this->validate($request, $rules, $customMessages);

The problem here, we cant specify what index of array that is duplicate. How can we specify the index of array like:

The bla 10 is duplicate custom message here