@Alfintoo After taking a look at your Premium Family subscription, it doesn't look like the second person you've invited has accepted their invitation yet.
If you've already sent an invite to a family member and they haven't received it, make sure that:
You've sent the invite to an email address your family member can access (not necessarily the email address on their Pandora account);
They check their spam folder, as the invite may have ended up there.
Once they've received your invite email, they'll simply select Accept Invite, and log into their existing Pandora account using the email address their account is registered under.
Hope this helps!
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