There are two different words spelled leis.
One is a prepositional pronoun, a combined form of le and sé. The full set of prepositional pronouns for the preposition le is:
liom, leat, leis, léi, linn, libh, leo.
Tá tú ag éisteacht liom - "You are listening to me"
Tá mé ag éisteacht leat - "I am listening to you"
Tá mé ag éisteacht leis - "I am listening to him/it"
Tá mé ag éisteacht léi - "I am listening to her"
The other is how you spell le before a definite article - le+an -> leis an, le+na -> leis na.
Tá mé ag éisteacht leis an raidió - "I am listening to the radio"
This is an Irish to English exercise, so you can only answer in Irish when it comes up as "Type What You Hear", and Tá mé is not correct in that case (that type of exercise should be called "Type What She Says").