Hi, thank you for writing a reply to me.
I already identify the error. I’m using “Email verification on signups” plugin to make sure only legit user can sign up with my website. When new user created, they needed to click the verification link sent to their email to confirm verify their email.
I’m considering to modify the back-end script to fix this issue.
Or, it would be nice if you can add a field on user’s “My Wallet” to insert referral link.