You probably know the answer to this by now, but for anyone else wondering the same thing here's a short little conjugation table. Willen is a slightly irregular verb, which makes things confusing.
willen (to want)
ik wil / je wilt / hij, ze, het wil
we willen / jullie willen / ze willen
You can also say "je wil" and it would be fine in certain regions, but this course teaches "je wilt".
wil is used for first person singular e.g. "ik wil een appel" (i want an apple) wilt is used for 2nd person singular e.g. "jij wilt een appel" (you want an apple) however, when asking a question, 2nd person singular drops the "t" e.g. "wil jij een appel" (do you want an apple) rather than "wilt jij een appel" hope this helps
"Jij" should have been accepted. You are sure the mistake was with "jij" and there was not another mistake in the sentence?
If it indicates again that "jij" is incorrect use the report function and highlight "my sentence should have been accepted". That way the moderators can see what your sentence was and will see if there might be a bug if "jij" does not get accepted.
Yes, if it is a listening exercise you have to type what is being said. Since there is a difference in the pronunciation you can only fill in je if the voice says je, and similar with jij.
Je is pronounced as in this sentence a bit like uh - juh
The ij of Jij is pronounced like ei(egg) and suppose in English the closest sound is eye.
You can check out this website which discusses all the different pronunciations and has audio for all of them: http://www.heardutchhere.net/DutchPronunciation.html