One of the worst things that can happen to online retailers is a transaction not going through because of something wrong on their end. If a customer can’t make a purchase because of a declined card, even though they have the funds to pay and the card is not fraudulent, it’s likely they’ll give up and the retailer will lose that sale. It’s a bigger issue than most merchants realize and can account for a substantial loss of sales every year.
Smaller merchants that sell globally tend to have this issue more than big-box retailers. They tend to use one bank for all sales, but if a transaction is declined, they have no fallback bank to try again. And usually it’s not the retailers’ fault, but the bank not allowing a transaction to go through for many different reasons.