Actually, there is no way for doing that without hacking the code of the extension. Try the solution below :
1. Open the file components/com_eventbooking/payments/os_paypal.php
2. Find the code below :
Code:
$this->setParam('amount', round($data['amount'], 2));
3. Change it to :
Code:
$this->setParam('amount', round($data['amount']*1.03, 2));
After that, it will work as expected.
Tuan
