Downloaded Instant Action maps are unzipped into Roaming\LancerTactics\custom\instant_action, so you should be able to manually put the combat_xxxxxxx.json files there and have them show up in the list.

I was also able to reproduce your crash – it looks like it happens when you don’t have that above folder before trying to download a map. You can create it manually or save a single custom map in the map editor and the game will create the folder. This feels like a high priority bug so I’ll try to make a new build with the crash fixed ASAP.

In testing this, I noticed that it looks like the list in Instant Action doesn’t update with the new maps until you close and re-open Instant Action, as well. Logged that as an additional bug.

Thank you for the report! Please lmk if you run into any more problems.