App can't download file. Throw SecurityException ("No permission to write ...")

My app download a file from URL and save it in /storage/emulated/0/AppName/file.db3. In Android 5 I have no problems but in highers versions (7 for example) when the download stars, the app throw the excepcion.

Error message

AssemblyInfo.cs (Android project)

AndroidManifest.xml

Android manifest (project options). I know that it's the same than AndroidManifest.xml

Is it possible that I missing any new permission in newest Android versions?

Thanks in advance.