If you hit the jackpot at the Marina Bay Sands casino recently, you'd likely find yourself being congratulated on the casino's website.
A certain Mr Chong was congratulated for having won a total of $215,032 at a slot machine on Jan 1.
Why is 'on' used before 'congratulated' in the first sentence, but 'for' is used after the word in the second sentence?
'Congratulated for' can be broadly synoymous with 'congratulated on'. But in the text you quote the word 'congratulated' just happens to fall next to 'on'. He might have been congratulated in an e-mail, or at a public reception, or after dinner... the preposition is up to you! In this case, though, he was congratulated on a website. He could, rather inelegantly, have been congratulated 'on a website on his good fortune' - the second 'on' there does belong to the 'congratulated'.