coupon just for new user, just create new account and redeem $50 free from github.
It works also on old account as long the account is not yet redeem any code.The $50 code yes it free but you need to find and edu mail or buy it so the thing is nothing is free and you need also a credit card,VCC or paypal on registering new account in Digital Ocean which one thing is not free..So the word "FREE" is not yet usable every thing is a price.