Variant Map for App Slicing

I’m trying to setup a project for iOS App Resource Splitting, but I’m unable to configure anything in Player Settings. I enabled “use on demand resources”, which unhides the “Variant Map for app slicing” option. However, when I open that up, I can see the list dropdown but the + button (which has a little arrow on it) does not do anything.

I’m guessing this is where I’m supposed to define my variants. but for some reason, I’m not allowed to add any variants. I assume there’s another setting somewhere that I have to enable first, but I have no idea what it is.

I’ve got AssetBundleManager in the project. Simulation is disabled. Local Server is currently enabled, but I’ve tried with and without. The project is set to iOS. iOS 9 is set as the target OS version. The AssetBundles are all built (and tested). I’m just not sure what I’ve missed.

Have you configured any variants on the asset bundles you have? Like explained in the documentation you have to pick tags for the asset bundles and “file extensions” for the variant options for each of the asset bundles. When you select the asset bundle in the inspector in the bottom there’s “Asset Labels” section, via the second drop down you can create and select the variants (say hires and lowres). Use short lowercase names as these serve as the file extension for the final asset bundle variant. Once you have a few of these and have assigned asset bundles to them, you should get the ability to create the variant map in the player settings.