When trying to send files not created by my app to Firebase Storage, I get an exception with the message "/path/to/the/file permission denied".
However, when I create in my code a file in the internal directory of my app (/data/data/package_name/files/) and send it to the Firebase storage it works.
How to send other files located elsewhere in the internal storage without troubles ?
You should add permission in the manifest and also check and ask for permission to access storage in the runtime.
In manifest, add:
<uses-permission android:name="ANDROID.PERMISSION.WRITE_EXTERNAL_STORAGE" />
For runtime permissions, I hope this library will help you. https://github.com/nabinbhandari/Android-Permissions