How is Value Added to a NSW Opal Card?

I purchased an Opal Smart Card for NSW public transport at a newsagent for $10 and was told it had $10 credit on it, but it did not. Registering the card online and attempting to add to the balance did not work either. The $40 top-up I requested was returned (with an SMS message saying:

The top-up requested on DD/MM for Opal card ending in 9999 wasn't collected and has been returned. Please do not reply to this SMS.

No explanation of "collected" was provided. But this may indicate that the card has to be used within a few days of money being added. My reason for getting the card was to travel from Sydney Central Station to the international airport by train. The buses in my vicinity are not equipped for the Opal card, so there is no reason, or way, to use it before then.

 

While the Victorian "Myki" smart card had some problems, at least I was able to put some money on the card and not have the money vanish.