"Nós precisamos de ações, não palavras."

Translation: We need actions, not words.

[Marjolein2020]

you can also say: We need actions, no words.

[Danmoller]

If this "no words" is an order, like "I don't want to hear any words", better translatios would be "sem palavras" or "nenhuma palavra".

"Não palavras" cannot fit that meaning. In fact, this alone has no meaning at all.

"Não" cannot modify a noun like English "no" can.

This "não palavras" in Duolingo's sentence makes sense because it contains hidden ideas: "Nós precisamos de ações, não (precisamos de) palavras."

[emeyr]

"We need action, not words" would be more usual speech.

[Lingledingle]

They accept "action" here.

[sheehanphoto]

"We need of actions" or is it really "we are in need of actions."