I'm new to simple planes (but certainly not to modding), and I've tried subscribing to a few mods. However they're not appearing in-game. I've tried restarting the game and Steam to no avail.

I get the welcome message from SimplePlanes informing me that mods have been added, but not of the items they add appear in "Build & Fly" from the Sandbox menu.

Is there something I am missing or doing wrong?

I should mention that I've no external mods installed, just the ones I'm trying to use through Steam (none of which have worked)