"The key provided seems to be invalid. Please check again."

[alo]

There’s no official app for Wanikani. Judging by the screenshot, is that Jakeipuu?

If so, the official thread for that is here:

[iOS/Android/Windows] Jakeipuu

This is a third-party script/app and is not created by the WaniKani team. By using this, you understand that it can stop working at any time or be discontinued indefinitely. I’m not a native English speaker so any grammar or wording corrections are welcome It’s a native iOS/Android mobile application for doing lessons and reviews. Features (inspired by Tsurukame, Flaming Durtles and Userscripts). Light / Dark mode Kanji stroke order Cherry pick words you want to …

For API key issues, check that you don’t have any spaces in the key when you copy paste. The other thing would be to check the thread and see if they’ve added APIv2 support. It looks like the app hasn’t been updated in a while so you may want to use an alternative.

The main recommendations for up-to-date apps are Tsurukame on IOS and Flaming Durtles on Android.