I recently updated the API key for WaniKani, and so it happened, a cascade of destruction. My KaniWani stopped updating of course. Yet I cannot seem to update the API key in the KaniWani settings.
This is strange. It should work. The only thing I can think of is the key might not have been copied properly. A character may be missing or something. If this is not the case then I suggest you contact the developer. There is a “contact” option on the KaniWani site.