PayPal\Api\Refund::setAmount PHP Method

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

 public function refundSale($saleId, $refundAmount, $currency = CurrencyConst::EURO)
 {
     $apiContext = $this->connectionService->getApiContext();
     $amount = new Amount();
     $amount->setCurrency($currency)->setTotal($refundAmount);
     $refund = new Refund();
     $refund->setAmount($amount);
     $sale = new Sale();
     $sale->setId($saleId);
     $refundSale = $sale->refund($refund, $apiContext);
     return $refundSale;
 }