While the top of the description notes that Citadel is required, Cloud Storage is not actually marked as requiring Citadel in CurseForge, which means that CurseForge's dependency management does not work correctly.

Had this issue as well and would love to see it fixed - every time I recommend this mod I have to let them know to go looking for what version of Citadel they need and install it separately, which is a bummer because CurseForge does that automatically for most things.