Congratulations!
Chai means an exclamation in "Nigerian Pidgin" Usually use to sympathize or to show how big of a deal something is.
E.g
He bought a mansion in Los Angeles, and you wouldn't believe how much he paid for it, Chai!
E.g
Mostly used in Nigeria comedy skits ( popular across Asia as well ) to signify how stupid/dumb someone's opinion or action is.
I use the word everyday myself.