You obviously got charged overseas currency usage. How much was it?
the emperor norton walking tour was USD19, my credit card charged SGD24.22
the cycling trip for 2 was USD55, my credit card charged SGD70.12
I'm not sure about any overseas currency usage charge, it's probably factored into the converted rates already.
Honestly, I was just able to add my DBS credit card into the US groupon account without any problems. I don't know how I was able to do so, but I did and it just as easy as signing up for a SG groupon account.