a member of family premium cannot accept the invitation

[oeuvreii]

just now I have purchased the premium for family for me and my girlfriend - everything went fine, the payment went through except when she got her mail and clicked "accept invitation" the link redirected her to her spotify account website saying: 

"Unable to join this Family plan. Try again by clicking the ACCEPT INVITE button in your email. If that doesn't work, ask the plan owner to send another invite."

we went through the forums searching for an answer, we tried fixing it by changing the default email address which was outdated and different from the one I sent the invitation to, then, after changing the email address successfully, I proceeded to send an invite to her new preset email address matching with the one shes registered with on spotify which again didnt work showing the same text as above.
were absolutely clueless, any solution?