[1.2n - Oceania] Conquering islands - asset construction

[toronovirus]

Is there some particular requirement before constructing assets on islands? I notice it says "Zone in Conquest", but having conquested the entire islands with no enemies present, and also entirely within a single sea zone, there doesn't seem to be a way construct some assets.

[toronovirus]

Nevermind, found the answer to this in the manual after another look (FYI it's by having the MTH built a makeshift port via the strategem).