When trying to activate the chroma hills hd texture pack, that is included in the realms plus subscription, it says error occured, and won't ever work. This should be fixed. I mean it's realms plus content and doesn't work with a realm.
Also imagine buying that and it doesn't work on your realm. Totally annoying
There is no known issue with Chroma hills pack. Try downloading a backup of your realm, resetting it and reupload the copy. If that doesn't work there might be something wrong with your realm, and you should reach out to our support. Closing this ticket.