As the title says if you're trying to redeem the "SEGA Mega drive" giveaway and it doesn't works with Google Chrome displaying the message "an error occured please contact your administrator" then use Microsoft Edge to login to your account and redeem your stuffs (it works flawlessly there). 

Alternatively, I have heard that Firefox works fine too but since I don't use Firefox in general and didn't wanted to install a new browser just to redeem a giveaway I highly advise anyone who is still facing the problem try my suggestion out.