If you’ve been invited to Buffer Publish as a user, your own Publish account will be on the Free plan. You do not need to be on a Premium or Business plan yourself, as you’ll have access to all the Business plan features for any social channels you’ve been invited to.
You’re also able to connect your own social channels within the limits of the Free plan, which is up to three channels, excluding Pinterest. Any channels you connect will only be available to you, and cannot be shared with other users.
One caveat to this is if you’ve been invited as an Admin on the Business plan. Admins on a Business plan are able to connect channels to the Organization. In this case, when connecting or reconnecting a channel, you would need to make sure you're working within the right Organization.
To see your Organizations, click the drop arrow next to your profile to open the account menu. From there, select the correct Organization. Once selected, your dashboard will refresh and those channels will now be accessible to you.
Now you can click Manage Channels at the bottom of your dashboard to connect new channels or reconnect channels that have become disconnected.
If you notice that some of the channels you have access to have been locked, this will likely be because the owner of the Business plan downgraded their account. When a Business plan is downgraded, the account is moved to the Free plan, on which fewer channels are allowed, and additional users are not supported. This is the reason those channels become locked for you.
In this case, you should chat to the Business plan owner and see if they had intentionally downgraded the account. It’s possible they didn’t know that downgrading their account would stop you from being able to access those channels.