PayPal\Api\RefundDetail::setAmount PHP Method

Amount to be recorded as refund against invoice. If this field is not passed, the total invoice paid amount is recorded as refund.

public setAmount ( PayPal\Api\Currency $amount )
$amount	PayPal\Api\Currency

    public function setAmount($amount)
    {
        $this->amount = $amount;
        return $this;
    }

RefundDetail