I just read through the Circle Casting description in the new Forgotten Realms: Heroes of Faerun book, and I'm a little confused about something. Under Secondary Casters, it says: "After you initiate the spell, each secondary caster takes the Magic action to contribute to the spell." But under several of the Circle Casting Options, it states "Each secondary caster contributing to the spell must expend a spell slot (no action required)."

Is this intended to override the first rule in these options? i.e., does the secondary caster simply mark off the spell slot, but they can continue to use their Action for something else? There are 6 options and half of them have this override, so I would have expected some language in the initial rule that says something like "unless otherwise specified".

I would assume that the use of a spell slot is in addition to the action.

It doesn't seem like an "override" to me. It seems like in all cases, secondary casters must take the Magic action; in some cases, they must also expend a spell slot (which does not require any additional action to be taken).