Paths are case sensitive
There is no such path called /download, it is called /Download
Also what kind of files do you want to upload? Media files or non media files?
See again Some basics on Android storage system
For non media files you need SAF as already mentioned earler
What about showing us a Do it result of your complete path?
Use the companion app and Do it to debug your blocks, see also tip 4 here App Inventor: How to Learn | Pura Vida Apps
see also Live Development, Testing, and Debugging Tools
Taifun
Trying to push the limits! Snippets, Tutorials and Extensions from Pura Vida Apps by
Taifun.
