By using Jadx and decompiling the WatchPower Android APK, I reverse-engineered its authentication process to have direct access to the backend's Rest-API. This way, we can programmatically query inverter data. I've made this available through a Python package in pip:
pip install watchpower-api
Check the examples folder for how to use the library. To run examples or develop for this library its best to use Poetry. Clone the project and run:
poetry install
It should install all necessary dependencies.