This is the exact path i use in my code dirrootexternal to acces it It's assigned as sd card memory but since it's a androidbox i am testing code on ít's solderd on the board
You can use this code to delete a folder recursively (be careful...):
B4X:
Sub DeleteFolderRecursive(Folder As String)
For Each f As String In File.ListFiles(Folder)
If File.IsDirectory(Folder, f) Then
DeleteFolderRecursive (File.Combine(Folder, f))
End If
File.Delete(Folder, f)
Next
End Sub