CotnraObjects.php

<?php

class Money {}
class Dollars extends Money {}

class Customer
{
    protected Money $account;

    public function putMoneyIntoAccount(Dollars $sum): void
    {
        $this->account = $sum;
    }
}

class  VIPCustomer extends Customer
{
    public function putMoneyIntoAccount(Money $sum): void
    {
        $this->account = $sum;
    }
}