PayPal\Api\RefundDetail::setTransactionId PHP Method

The PayPal refund transaction ID. Required with the PAYPAL refund type.

public setTransactionId ( string $transaction_id )
$transaction_id	string

    public function setTransactionId($transaction_id)
    {
        $this->transaction_id = $transaction_id;
        return $this;
    }

RefundDetail