A social account can only be connected to one Social Set across all Pallyy accounts.
If it’s already connected to another Pallyy account, either by you or someone else, you won’t be able to add it again until it’s removed.
To fix this, log in to the Pallyy account where it’s currently connected, remove the social account, then return to your current account and try again.
If you do not know which Pallyy account the social account is in, contact live support with the name of your social account and which social network it belongs to (eg. Instagram, Facebook, X...)