The official Gluon docs say in the prerequisites for an Android build:
From the Android SDK Manager, install...from Extras the Android Support Library
However, it seems that this is retired from the sdk manager in lieu of the "Android Support Repository", a gradle repository. The javafxports plugin is apparently still looking for the old support library folder in the android SDK, as indicated by the error:
Cannot expand ZIP '<my AppData path>\Local\Android\sdk\extras\android\support\multidex\library\libs\android-support-multidex.jar' as it does not exist
which has this stackoverflow answer, indicating the sdk doesn't install it there anymore, even with "Obsolete" checked in the sdk manager. How can we get the javafxports gradle plugin to find the support library while it runs the 'android' build task? Sure we could manually move it there, but that'd be a really ugly process for using with a build server or dev team...