Duolingo uses 3rd party commercial text to speech engines to read the exercises in most of the other languages. There are no 3rd party commercial text to speech engines available for Irish, so, instead of leaving the Irish course with no audio at all, Duolingo arranged for over 4,000 exercises to be recorded, and manually attached these recordings to the relevant exercises.
The website and the various different mobile app versions of Duolingo all use the same set of exercises and audio files.
Why is it not here?
Obviously because that verbix site isn't a reliable site.
(You don't even have to know what the correct conjugation to know that there's a problem with that page - the leathan le leathan, caol le caol/"broad with broad, slender with slender" rule is being violated all over the place).