P.S. Maybe there was a limited time or limited number of bonuses. Advice to everyone then, as soon you see something, immediately grab it after checking if everything is legit.
You should check your email, I heard from a friend with the same case as yours. He said that Stake sent him a correction email for the bonus and he can claim the bonus but he did not tell me the amount of the bonus from the correction email so I have no idea if he get the same amount as offered on the first email ($20) or he get smaller amount. Judging from the word used on the email "correction", I think it can be a correction for the amount or correction for the link.