Cannot Place Spy on Enemy Planet

I am trying to place a spy on an enemy planet. I select the planet I want to place the spy on, and hit the place spy button. However, when I do this I get a pop-up screen that says I cannot place the spy because my spy isn't advanced enough to be placed on a planet, or some similar message. Do I need to research the additional espianoge technologies to level up my spies before I can place a spy on a planet?  Alternatively, if I assign my spy to the enemy civilization via the espianoge screen, will that level up my spy eventually? And if so, how long until the spy is a high enough level to be placed on an enemy planet?  More generally, is there a post or website or something that explains the espianoge mechanics in more detail? I didn't see espianoge addressed in the game manual and the only developer post about espianoge I can find is from the Crusade release. But that post is more of a general overvirw, not an in-depth description of how the mechanics work. I have the base game, Crusade, Merceneries, Precursor Worlds, and the Intrigue expansions installed through Steam.