We can use this form when we talk about future - "вы возьмёте / ты возьмёшь такси" (you will take a taxi). But in present continuous it is almost always "вы едете / ты едешь на такси". Usually we speak "вы едете / ты едешь в такси" only when we want to clarify that somebody rides exactly inside the certain taxi or in another clarifications. Please correct me if I am wrong. And I think that here the programm writes "в" but not "на" because in English a preposition "on" use only with words "foot" and "horse".
LOL, I forgot to change back to English keyboard and I accidentally typed "ёу го бытажи" (Russian mnemonic keyboard layout).
"Interestingly", it wasn't accepted...
A suggestion here: In similar cases other courses in Duo allow to type the answer again saying something like "Oops, it seems your answer was not in English."