spa-js-api/app/Exceptions/ApiException.php

<?php

namespace App\Exceptions;

use Exception;
use Illuminate\Http\Exceptions\HttpResponseException;

class ApiException extends HttpResponseException
{
    public function __construct($code = 422, $message="Validation error", $errors=[])
    {

        $data=[
            'error'=>[
                "code"=>$code,
                "message"=>$message
            ]
        ];

        if ($errors) {
            $data["error"]["errors"] = $errors;
        }

        parent::__construct(response()->json($data, $code));
    }

}