You can gain a Catamaran Qualification by
(i) Completing the NauticEd Catamaran Sailing Confidence course online
(ii) logging at least 3 days as skipper or 7 days as crew on a 38 ft (11.5m) or greater sized catamaran
(iii) being Bareboat Charter Master Rank with level III experience
OR
You can gain a Catamaran Endorsement by
(i) Completing the NauticEd Catamaran Sailing Confidence course online
(ii) successfully complete an on-the-water half day (4-5 hours) Catamaran Endorsement assessment on a 38 ft (11.5m) or greater sized catamaran with a NauticEd Assessor.
(iii) being Bareboat Charter Master Rank with level III experience
The difference is that a Qualification means you have enough experience to automatically qualify without an on-the-water assessment whereas an Endorsement means that you have been assessed on-the-water as to your competence and successfully passed. The endorsement is considered of higher value because of proven competence.