"What kinds of cities do you like?"
Translation:Milyen városokat szeretsz?
Adjectives that are in front of a noun, modifying it, do not take plural or case suffixes.
The english said you. So it should be you Te or also you plural Ti but this last one was not accepted
1) did you also use the verb ending for ti, or did you use ti szeretsz?
2) it may be just a missing alternative - this couse still has a lot of correct sentences that are not accepted yet. Report them to bring them to the attention of the course maintainers.