What is the first thing the developer should check?

A developer identified a use case where a triggered send of an email is needed. The developer already successfully set up authentication with a Client ID and Client Secret has used them in several REST calls. When the REST call is made, a "401 Unauthorized" error is returned.

What is the first thing the developer should check?
A . The send permissions have been granted for the Client ID and Client Secret within Installed Packages.
B . The email interaction has been started
C . The automation permissions have been granted for the Client ID and Client Secret within Installed Packages.
D . The email interaction has been published.

Answer: A