Device Limit Reached on card - only on one device

There is a limit on how many cards can be added to your Wallet. There is not an exact number as it has changed and depends on the storage you have available in your Secure Enclave, but at last reports it appears to be about 16 cards. Do you have that many cards in your Wallet? This includes a transit card or passes too.

Ok, just making sure. Here is the Apple Support number, but be prepared for them to say you need to contact the card issuer, since it is not Apple that approves or denies a card when added.

Contact Apple Support - Apple Support

It may be an issue with T-Money if the Chase card is not one issued in South Korea according to other users who have tried:

T-Money integration doesn't support foreign credit cards (according to the press release, "in order to add money to the T-money card from Apple wallet, such as top-up or automatic top-up, you must have a credit card or debit card issued in Korea."