It isn’t explicit in our documentation but it isn’t possible to use AssetBundles with encryption keys in FMOD Studio.
When using FMOD Banks in Asset Bundles, first the asset bundle needs to be loaded using the UnityWebRequest system and then the data needs to be loaded by FMOD using loadBankMemory.
loadBankMemory is not compatible with encryption keys but needs to be used because the data returned from the UnityWebRequest.downloadHandler is a raw byte array stored in memory rather than a file from disk.