If you sent your friend a referral link but it didn't work, they can still enter the code manually within the first 24 hours of account creation! They can enter this code here: Home > Enter Code. This button will be to the left of the "Invite" button in the middle of the screen. This should link your accounts and you'll get the boost when you're both mining!
If this still doesn't work, then here are some common reasons:
Your friend has had an Ember account in the past
Your friend's Ember account is older than 24 hours
Your friend has already been referred by a different user
Your or your friend's device has multiple accounts linked to it
If you successfully added a referral code, but your friend is still missing on your end (or vice versa) then it's likely that one of your devices has multiple accounts tied to it. In this case, please send the email addresses tied to both your and your friend's Ember account to our Support team.