Your brand-locked virtual card can only be used at the merchant where you made your first purchase. If used at another merchant, it will be declined.
Using a Fluz virtual card is just like using any other card. When shopping online, simply:
Add your items to the cart.
At checkout, enter the card number, expiration date, CVV, and billing address from your virtual card.
Complete your payment with your selected brand.
You will only be charged at the time of purchase, not when you created your virtual card.