I have finished the research for the relevant ships e.g. a corvette but I cant build it. It has a red circle with a line across it in the production menu saying "One of the following modules is missing" but does not actually give any explanation as to why I cant produce the ship.

I have seen some references to a treaty of some sort (similar to London treaty in vanilla) but I cant find any in-game reference to this treaty. Just some comments from people.

How do I build ships?