A card can only be updated if you have enough available credit limit for the outstanding plan value.
When you update your card the Splitit system will attempt to authorize the card for the outstanding value of your installment plan. Not having enough room on the new card for the authorization is a common reason a card update fails. If you do not have enough available credit on your card you should make room on your card and then try the update again. Remember, only attempt a card update twice in any 24-hour period.
If you are unable to make room on your card for the authorization you may need to use an alternate card for the required update. You can also choose to pay off the plan in full with a debit card.