Considering that their domain is for sale ((
https://whois.domaintools.com/bitoffer.com) + the continuous winnings, it's most likely a trap.
bitoffer.com is for sale!
This domain is listed for sale at one of our partner sites for $6,410.
It's a common scam story, the exchange sets up bonuses/use of demo accs to attract new users -> make them feel it's super easy to make money in their platform -> user bites the bait and deposit -> exchange proceeds to suck their money.
I wouldn't risk a cent nor my time.