There are a couple of reasons why you might not be able to order a personalized card.
If you have already used up your allotted recards your attempted order might be charging you a fee. You will need enough of a balance to cover the fee. You can wait for a payment to come through to your account and try again later.
It's possible that your employer has not yet introduced personalized card ordering options. But no need to worry, this feature is likely to be available soon!