How should I invite my friends? I tried once but I didn't receive spirit stones? Or do I need to invite specific number of people?
Friend Invite
StaticNight9 They need to make an account through the link you gave them. If they make an account through the app or the website without passing through your link it wouldn't count as your invite. Hence, you won't get any spirit stones :( Learned this the sad way 
5 days later
DaoEternal i have tried as you say my friend, but it didn't work. i send an invite to my friend and he used the link i gave to him. That link was the link the system sent to him. But I didn't receive any stones.