<?php

declare(strict_types=1);

​

class User

{

    private int $totalSpent = 0;

    /** @psalm-internal Payment */

    public function addToAmount(int $amount): void

    {

        $this->totalSpent += $amount;

    }

}

​

class Payment

{

    public function __construct(

        public readonly User $user, 

        public int $amount,

    )

    {

        $user->addToAmount($amount); // all good here

    }

}

​

$user = new User();

$user->addToAmount(20);