The present disclosure relates to a method for providing a payment agency service and a server using same, and a method for registering an authentication certificate, a method for providing a payment agency service, a card company server, and a payment agency server. The method comprises steps of a payment agency server: (a) delivering identity authentication information and a first push token ID delivered from a user terminal to a card company server; (b) delivering a successful authentication result to the user terminal to support generating and saving a public key and a private key of the user; and (c) managing the first push token ID or a second push token ID as an integrated push token ID when the first push token ID and the second push token ID match, and saving registration information including the integrated push token ID and the public key.