Did you consider using the official [threema-android Java implementation of an API client](https://github.com/threema-ch/threema-android/tree/3d71e001e7301cb5f3bef09b51cfa5dfea860c10/app/src/main/java/ch/threema/app/services)? It seems considerably easier to me than relying on [bluec0re/threema-rs](https://github.com/bluec0re/threema-rs), an outdated 3rd-party reimplementation.
Did you consider using the official threema-android Java implementation of an API client?
It seems considerably easier to me than relying on bluec0re/threema-rs, an outdated 3rd-party reimplementation.