A virtual card is issued the moment you ask for it — there is nothing to post and nothing to wait for. You choose Visa or Mastercard at creation, which decides the card's BIN, and you set how much of your ZikCards balance to load onto it. The card can spend up to that amount and no further, so it cannot be overdrawn and there is no credit to repay.

To a merchant it looks like an ordinary US card, because that is what it is: the cards are issued in the United States and run on the Visa and Mastercard networks. You can top a card up whenever you like, freeze it if something looks wrong, and close it when you are finished — closing returns whatever is left on it to your wallet.