"This coffee is good" was not accepted. Anyone?
This is a different sentence. "Ta káva je dobrá."
Maybe so, but in English this is interchangeable. Both should be accepted.
It won't be. Be prepared that this distinction will be observed in many other sentences in this course.
Is it "dobrá káva" and not "dobrou kávu" becausenin this lesson coffee comes in as a nomitive and not an accusative? Like voda/vodu?
I learn on my phone so the tips don't show up.
Yes, they are nominative forms,. You can access the Tips and Notes on a mobile device by getting to Duolingo through a mobile browser. They are not currently available in the apps.