I have sent several invitations to both my daughters.
They do get the invitation email, after several tries, they are able to click the link to "accept invite". But they get routed directly to my account site, and there is no possibility to accept the invite.
The invite is sent from my laptop, and they try to accept it on their Iphone7 devices, and I have made sure to be logged out of my account, before they click the invitation link.
See attached screen photos from my daughters devices, that show invitation e-mail with link and my Spotify account screen they get routed to via the link.
Unfortunately I'm only able to attach one screen shot!
*Community Rock Star edit - removed payment/personal info*