Greetings from Goibibo.com!!
Please note that the referral code shall be applied while creating an account. However, you may still earn Gocash by referring your friends to download the app using your referral code. Also, you may sync your contacts and ask them them to sync with your number as well to earn Gocash plus. You may also share your registered email id / phone number / referral code along with your friend's who referred you so that we can check. Thanks