When you share the unique referral link or code, you need to ensure that your friend uses this referral code to sign up. If not, your friend's account will not have you mapped as a referrer.
In case your friend has used any other person’s referral code or clicked on any other person’s referral link instead of yours, then in that case the one who introduces your friend originally will be receiving the reward for that friend, and not you.
It is very easy to track which of your friends have joined Dhan with your referral code.