When you have questions, it’s probably better to just upload the things in question to your Github and ask. Folks’ll probably help out if they’re able, and it helps a lot to see all the stuff in question.
If your location uses a terrain that already exists, only adjusting the weight should be necessary, since that location already spawns in the game. Just make sure the “om_terrain” line in your mapgen entry matches the “om_terrain” of the location you want it to spawn as. IE: A new grocery store layout would already spawn, so long as your location also had the “om_terrain” line of s_grocery.
If your location is completely new, make sure you’ve set up both the overmap_terrain entry AND an overmap_special entry. The terrain tells the game how the location should look in the game map, but it doesn’t handle spawning. The special tells the game how to spawn that location (the where and how and how often, etc).
If you’ve done all of that, check the occurrences line in your special and set it to something absurdly high so it will spawn a lot for testing. IE:
"occurrences": [ 5, 20 ],
So, that’s my scattershot answer. Hopefully one of those was the issue.
Either way, again, I’d advocate for Github. I know you want to keep things secret for a big reveal when it’s ready, but more people will respond if they can see the problem in front of them.