* run rsync tasks repeatedly with JobScheduler API
* NO ROOT NEEDED
* AD FREE
There are users' reports saying it is not possible to sync on external SD Card with Android 6.0+.
According to Google's document:
It is true if you did not format the external SD card as adoptable storage but left it as portable. Doing this made any 3rd party apps, including RsyncWrapper, failed to write contents to this card freely. The directories on the SD Card that an app can write to are restricted to the following places, for example:
In RsyncWrapper, when you enter the source/destination field, you can now use the built-in directory chooser to help finding out these writable directories with ease.
Sorry for inconvenience.