While searching for a particular course to add it to a Certification, you are unable to view the course under the catalog.
There are three enrollment type in Learning Manager:
Learners can directly enroll themselves to these types of courses.
These courses must be approved by Managers. Learners can sign-up for these courses, but they are not enrolled directly to these type of courses without Manager’s approval. A notification request is sent to Managers when learners sign-up for these types of courses. Upon Manager's approval, these courses will be listed as enrolled for learners.
These courses can only be nominated by managers. A Learner cannot enroll to these types of courses.
In a Certification, you can only add self-enrolled courses and not Manager nominated or Manager approved courses.
This is a default behavior in Learning Manager.