"Tonight we are doing the same thing."
Translation:Vanavond doen wij hetzelfde.
I wrote vannacht instead, and it was considered wrong. Whereas earlier in the course, the translations were quite strict with (vanavond = this evening) and (vannacht = tonight).
Also I'm not sure if this is considered "reporting a mistake". If so, where is the appropriate place to write this, and what types of comments are appropriate for these comments sections?
Yes, I think that "vanavond" and "vannacht" should both be accepted as translations for "tonight".
The best place to report things like this is to click the "Report a problem" button after your reply is marked by Duolingo (during a lesson or practice session). Unfortunately there is no way to do this after you have moved on to the next question, except for retaking the lesson and hoping to get asked again.
These sentence comments are a good place for new learners to ask questions about grammar, translations, or anything else that they confused about.