Oops!
Be aware that if you are trying to sign up friends and family onto this platform, that they should look for their welcome/registration email on a daily basis. Once the email comes from Steemit, you only have 7 days to register with that link. I recently tried to sign up several family members, and coached them that the approval process may take some time (as it had for myself, and also a friend that waited several weeks to be approved).
They didn't check their email for quite some time. When they finally did, they were all greeted with this dreaded Invalid Token response. As far as I know, there is no fix. Both the phones # and emails used to sign up will no longer be eligible for the free Steemit account. That means paying for one through the other existing services, which I doubt most unfamiliar people will do, or getting a new cell line temporarily/permanently to get a free account (not likely).
Moral of the story: this platform needs you to really want it, I guess. They're not just letting anybody in.