Just write your number and you should receive SMS or call with code. Or you can use app for smartphones called Authy.
same here...
do not work for me..
and i do not found any detailed hot to to withdraw my small btc balance!!!
i checked and it worked for me, i received SMS from them , luckily for me i didnt invest and also cashed out before

authy don't work for me...
and my cahs still on zencloud server....
really bad services...
hate zenCloud...