Why can't I use 'im' here?
That would be nice, but "im" only works for "in dem", and there is no contraction for "in der".
It accepted "der Nutzer lernt im Netzwerk" which I just guessed at.
network is netzwerk - why is this answer so counter-intuitive? totally not german
Netzwerk is a word borrowed from the English language. Many terms from the technology field have been borrowed and adapted the same way. Just look at "computer".