The helper text here threw me off a little. The lesson was trying to teach me lu', so when the helper text for qoplu' said is arrested. I mistakenly thought qop was an adjectival verb for is arrested, and then I tried putting the passive voice on top of that, especially with the object being 'Iv. I thoroughly confused myself, until I opened up boQwI' and learned that qop is the action verb arrest. I'm not sure what should be done differently, but I think this could be more instructive somehow.
The hint system in Duolingo is... non-ideal. It draws from various uses of the word through the course and occasionally does not even always show a direct match for how the word is being used in the current sentence. There are some tricks the contributors can use to help a little, but even those do not help consistently. I'll look into it and see if there's anything I can do.