PaymentCollection::getPaidSum

public function getPaidSum()
{
	$sum = 0;
	if (!empty($this->collection) && is_array($this->collection))
	{
		/** @var Payment $payment */
		foreach ($this->collection as $payment)
		{
			if ($payment->getField('PAID') == "Y")
			{
				$sum += $payment->getSum();
			}
		}
	}

	return $sum;
}