Please try this way

use Validator;public function store(Request $request){    //$data = $request->all();    $data = json_decode($request->payload, true);    $rules = [        'name' => 'digits:8', //Must be a number and length of value is 8        'age' => 'digits:8'    ];    $validator = Validator::make($data, $rules);    if ($validator->passes()) {        //TODO Handle your data    } else {        //TODO Handle your error        dd($validator->errors()->all());    }}

digits:value

The field under validation must be numeric and must have an exact length of value.

I see some helpful answers here, just want to add - my preference is that controller functions only deal with valid requests. So I keep all validation in the request. Laravel injects the request into the controller function after validating all the rules within the request. With one small tweak (or better yet a trait) the standard FormRequest works great for validating json posts.

Client example.js

var data = {first: "Joe", last: "Dohn"};var xmlhttp = new XMLHttpRequest();xmlhttp.open("POST",'//laravel.test/api/endpoint');xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");xmlhttp.send(JSON.stringify(data));

project/routes/api.php

Route::any('endpoint', function (\App\Http\Requests\MyJsonRequest $request){    dd($request->all());});

app/Http/Requests/MyJsonRequest.php (as generated by php artisan make:request MyJsonRequest)

<?phpnamespace App\Http\Requests;use Illuminate\Foundation\Http\FormRequest;class MyJsonRequest extends FormRequest{    public function authorize(){        return true;//you'll want to secure this    }    public function rules(){        return [            'first' => 'required',            'last'  => 'required|max:69',        ];    }    //All normal laravel request/validation stuff until here    //We want the JSON...    //so we overload one critical function with SOMETHING LIKE this    public function all($keys = null){        if(empty($keys)){            return parent::json()->all();        }        return collect(parent::json()->all())->only($keys)->toArray();    }}

Your payload should be payload: { then you can do

$this->validate($request->payload, [    'name' => 'required|digits:5',    'age' => 'required|digits:5',    ]);

or if you are not sending the payload key you can just use $request->all()