But Mutiny won't work inside the Spring itself for now, there are too many errors in console and it keeps crashing, I think it's related to wasm and service workers support inside WebViews, so it's not trivial to fix. You'll have to run Mutiny in Chrome or elsewhere.
Discussion
Actually, Mutiny seems to work inside Spring! The issues might have been with the emulator, it's all ok on a real device. I would not actually use it this way, Spring is too unstable to let it host your wallet, but if you're adventurous...