Translation:Vâng, tạm biệt
chào = salutation. Duo should accept it.
đúng = yes but to acknowledge something is correct.
tạm biệt = temporarily out of sight/temporarily apart. To me, see you later would be more accurate for this translation than goodbye.
In real life, we don't often say these things. We often say "tôi đi nhé," meaning "OK. I'm going" or "vâng, bạn đi," meaning "OK. I know you have to go," literally "you go."