When koala is being used as an AUv3 plugin, you need to explicitly give it some input. If you load koala as an instrument (i.e. in the top slot) it can’t get input – this is not the fault of koala, its a limitation of AUv3 plugins (and also VST plugins etc)*
In order to get input, you need to put koala in as an effect – i.e. the second slot down, and put in a microphone or whatever you want to sample from in the slot above, pls see picture below:
*please, please, don’t write a bad review because of this, its purely how ALL plugins work on ALL platforms, there is literally nothing I can do about it. I am happy to send a bribe if you need it, and also write to Apple, Steinberg, Avid and authors of all other plugin systems on your behalf to see if they will change how plugin formats work (I doubt they’ll listen though!)