What should the customer have in place to ensure this solution can be implemented?

A customer wants to set up a real-time, API-driven way to be alerted when transactional messages fail to send out of Marketing Cloud. They are currently in the process of hiring a full-time developer but want an implementation in place for the developer to maintain.

What should the customer have in place to ensure this solution can be implemented?
A . A Transactional Journey with the Not Sent Notification activity included
B. A Datorama instance to ingest their data
C. An external system to receive and confirm callback and subscriptions
D. An Interaction Studio instance to ingest their data

Answer: C

Explanation:

To set up a real-time, API-driven way to be alerted when transactional messages fail to send out of Marketing Cloud, Northern Trail Outfitters should have an external system to receive and confirm callback and subscriptions. Callbacks are notifications that Marketing Cloud sends to an external system when certain events occur, such as message failures or bounces. Subscriptions are requests that specify which events and messages an external system wants to receive callbacks for.

References: https://developer.salesforce.com/docs/atlas.en-us.noversion.mc-apis.meta/mc-apis/transactional-messaging-api.htm