OpeneBayParticipantInterface updateSubscriberCredentialsAPI request is triggered and delivered to your Open eBay App listener when an eBay user auth token that associated with your Open eBay App was renewed or revoked.
What is needed from my application?
You must implement this API and response with Success in ack filed as below indicating you have replaced the user's old token with the new token delivered in the updateSubscriberCredentials request so that eBay can set your application available to the subscriber in question.