same for me too. i don't why is this happening.
Failure to redeem redemption code, account has been signed
22 days later
Same for me my id is 4305293979 and my friends id is 4305007898. i got a referral code from my friend and didn't get my 20ss.
a month later
Likewise
18 days later
same happened to me :(
Me too. I can't invite.
same here as well...
seems like they don't care...
Well, the only way to gain SS is to buy it. Hayys.
zahi_7692 but I've been seeing reports that people are also having problems with buying Spirit Stones. I'm tempted but I'm scared that I'll be "scammed". 
Some said that it is to prevent people abusing the system.
I emailed webnovel and this is their reply.
On Tue, May 21, 2019, 3:52 PM service <service@webnovel.com> wrote:
dear，
Only new ID with new equipment can be invited successfully. In addition, the limit of invitees that can redeem rewards a day is 10.
Warmest Regards,
Team Webnovel
So it means the invited person need to have a new device. That is not registered in webnovel servers to avoid abuse of referral program.