I have talked to webnovel repeatedly and what they have said about the friends codes is:
1.The invite has to be a device that has never had a webnovel account or the app downloaded.
2. The code has to be entered within 7 days of the account being created.
3.If you have done the above and not received the SS, you will need to contact support and tell them -
1.both you and your friend’s(who invited you) User ID and User Name
2.the date you redeemed
3.the version number of our APP
4.the version number of your phone(Andiord or ios)（both of you）
So, to any existing users that want SS. You have 3 options.
1. Do the couple of tasks that get you SS daily.
2. Buy SS.
3. Find all the friends and relatives that don't have the app, invite them and record all the needed information in case you need support to get them when they don't arrive.