C-Cex API does not allow you to withdraw, it doesn't have that option.
you can check it out here: https://c-cex.com/?id=api

i must say what you want is not such a good idea, and it is not safe either. it is best if you use your own wallet and do the withdrawals that way. using an exchange like this to pay your customer can cause a lot of trouble, for example a couple of days ago they had a 30+ hour long maintenance for their bitcoin wallet which means no withdrawal for your customers!
or their site may go down for maintenance, and a lot of other trouble.