"Politicians are not important in these four countries."
Translation:Ebben a négy országban nem fontosak a politikusok.
Your word order is fine. Sorry it's pretty frustrating when they aren't accepted. :/
However: Most back-vowel adjectives take -a- as the linking vowel when you form the plural (this is different from nouns). So, fontosak is both correct and typical.
There are a few exceptional adjectives that take -o- as the linking vowel. I think the only ones that occur in this course are nagyok, fiatalok, olyanok, and maybe gazdagok. Two other common ones are vastagok (thick) and boldogok (happy).
I don't think I entered my word order while also spelling "fontosak" correctly, so maybe that was the only reason it was rejected. Next time I do that lesson, I'll try it again.
I guess I was confusing adjectives with nouns, which usually use "ok" as the ending for back-vowel words that end in a consonant. I don't think I've ever noticed that most of them use "ak." I probably just haven't seen enough examples of sentences where the adjective comes after a plural noun. Thanks again!