Because there is a direct object.
jI- indicates “subject = I, no object”
vI- indicates “subject = I, object = him/her/it/them”
Given the fact that you posted a reply rather than editing your comment, I fear you might be using the Android mobile app and are not aware of the tips and notes we have prepared for each lesson unit — which are only available on the website https://www.duolingo.com/ .
If so, I highly recommend that you visit the website before you start a new unit (you can probably even do so with the browser on your mobile device if you wish) and read the tips and notes first.
They are hidden a little: after you have selected the unit, you have to click on the little lightbulb icon to access them: