This are the values list that will be displayed in the mobile app during the creation of a new activity.
Learn more about External Activity Types: External Activity Types and Activity Subtypes
Example
Background setup requirements for enumeration value:
BD64: Make sure the distribution model includes this message type.
WE20: Make sure outbound parameters in partner profile includes this.
/PACG/ECM_NOAS - No Object Assignment : Make sure that the entries are here for the related company ID.