I have now managed to build apks for @Avacee's C# version and for the the original Velleman Java based app. The xamarin build environment on Linux for C# is complex and not very usable. Velleman's aWFS210 github repo contains a java based Android implementation that has not been touched for four years. The aWFS210 subdirectory of the main Velleman WFS210-App github repo is a port of the original java app to C#. This subdirectory is used to provide the Android APK.
My current idea is to backport the C# changes to the original java app. This gives me a much simpler Android Studio Java build process and removes the xamarind dependencies. I will create a new repo under rogerjames99 that will contain a standard Android Studio build environment.
As a wild speculation, I wonder if I could get a quote from Velleman to buy up their old stock which they seem to be dumping and then crowdfund a project to raise the cash.
Roger