My understanding is that script mods can not be nested. So they go directly into the Mods folder and not into a sub folder within the Mods folder. I may be incorrect in that assumption but this is where I place any script mods and I've had no issues.
To download and install this type of mod:
1. Click on it to save the file. Save it to a folder on your hard drive or USB key.
2. Copy the file from where you downloaded it to the Sims 4 Mods folder
C:\Users\Username\Documents\Electronic Arts\The Sims 4\Mods
3. Make sure both mods/cc options are check marked in the Game Options.
-- Options > Game options > Other - Enable Custom Content and Script Mods Allowed
4. You will need to exit the game and reload it for the mod to show as active.