"I do not think so."
Translation:Я так не думаю.
When translating Russian to English, wasn't "Я думаю нет" translated as: "I don't think so"? So why is it not accepted going the other way? Or does "Я думаю нет" literally mean: "I don't think", rather than: "I don't think SO"?
I really thought it was a gift when - as sometimes happens - I got the reverse translation of the one I'd just done, and was sure I'd get it right. So I was really surprised when "Я думаю нет" was rejected.
I'm pretty sure не needs to be with думаю and you were marked wrong for separating them with так. It would be like saying in English "I do not so think" which is just odd and awkward, or literally equivalent to "I not so think" which is complete nonsense.
Correct would be either Я так не думаю or Я не думаю так. Either way, you need to clearly be negating думаю.