Yeah, I couldn't tell either but then I also couldn't tell that it was "ag" in there. I wish the people speaking were taught to make sure they pronounce every word as you should do for someone trying to learn a language. And yes, I know that it is not how people really speak but people speaking French, Spanish and English do not pronounce every letter of every word either but their languages are not taught by the way people speak
Both forms are grammatically equivalent and correct, but Duolingo's "Type What You Hear" exercises can only accept one answer (because in most languages on Duolingo, the computer reads the script). If this had been a "Translate from English to Irish" exercise instead, it wouldn't have mattered which form you used.
As for dialect, Munster has historically favoured "synthetic" forms (táim, etc), and Ulster hardly uses them at all, preferring the "analytic" form (tá mé, etc) , but for the most common first person forms, it really doesn't matter which form you use - all Irish speakers will be familiar with them. Munster Irish still contains some synthetic forms that will confuse people who haven't encountered them before.