function execute_payment($payment_id, $payer_id)
{
    $payment = PayPal\Api\Payment::get($payment_id, apiContext());
    $payment_execution = new PayPal\Api\PaymentExecution();
    $payment_execution->setPayerId($payer_id);
    $payment = $payment->execute($payment_execution, apiContext());
    return $payment;
}