In Hindi : Ca - च , Cha - छ
In Nepali : Cha - च , Chha - छ
Actually, I think it is similar. Duolingo uses ISO 15919 romanisation while Indian Government uses Hunterian - similar to Nepali.
For example, the Indian state of छत्तीसगढ़ is written as Chhattisgarh.
You are might be right but in the nepali grammatically it is wrong while छत्तीसगढ़ written like Chhattisgadh