"No, no estoy bien."
Translation:No, I'm not ok.
Estoy is for something temporary e.g. estoy bien (i am well - but i could become unwell) vs Soy Pedro (i am Pedro)
Estar is used for temporary things: feelings, location, and also used as an auxliary verb for progressive. Ser is used for more permanent characteristics: description (personality or physical appearance, but not emotion), career, origin, or time. An easy acronym to remember for ser is DOCTOR; feel free to look it up as it may help you with this.
Bien is more like "fine" and bueno is more like "good". You would answer with bien to say how you are doing. Bueno is more with things.
No (estar-form) bien translates as unwell in other questions, but not here.
I know. The same happened to me. It's inconsistent and very discouraging! I hate Duo when it does that!
I wrote "no, no I'm good". I now understand the importance of punctuation marks.