As soon as the transaction payment is fully confirmed, sometimes instantly, we will send out the refill automatically. Once it's been sent you'll get a receipt email, and the top up should arrive instantly.
This is the case in most countries, but in some, there may be delays of up to 24 hours.
If you haven't received a refill, you can always reply to the receipt email we sent you or raise a ticket here and our customer service team will investigate the order.