You can be very much assured that any such "Bot" on telegram is a risky thing to deal with. If you want to buy sell coins, go to an exchange not some random username on the internet who promises you to sell those coins. These things always end up with a scam and you will be sorry for being so stupid when you could have prevented it.
I do agree that using Telegram bots for trading is very risky, but looks like Chatex is not just some unverified random scammy bot. I did some digging and seems like Dash partnered with Chatex to enable trade of Dash via their bot.
https://dashnews.org/chatex-p2p-cryptocurrency-exchange-telegram-bot-to-add-dash-with-instantsend/That of course is not a sign of legitimacy and OP should due his own due diligence before using something as Telegram bot for exchanging currencies.