Unless you are downloading files which are explicitely(1) marked being full modpack you downloaded zip which does not include mods, only pack medata data and configs. You can not import that that zip into third party launcher.
If you want to use those zips you must use third party tools to download mods and to build instance.
curse pack downloaders:
- https://github.com/DoubleDoorDevelopment/CurseModpackDownloader
- https://github.com/portablejim/curseDownloader
- https://github.com/Vazkii/CMPDL
- https://github.com/EfficiencyVI/adcmmp
- https://github.com/amcoder/curse_client
- https://github.com/CandiceJoy/CandisCursePackAssembler
- https://github.com/elifoster/mcfpm
- https://github.com/kaeedo/Cursed/
- https://github.com/peterix/curseDownloader
- https://github.com/Paleocrafter/CurseSync
(1) Example: https://minecraft.curseforge.com/projects/agrarian-skies-2/files/2261454#additional-files