How to Save files on external SD with Delphi XE8

Question

anybody knows how to write a file on the external sd card? i checked user permissions in the manifest file and it says user can write to external sd

but everytime i try something like

TFile.copy(src, '/storage/extSdCard/file.txt')

src is a file located in the internal device memory

i receive a permission denied error. Of course there is no error if i copy the file within the internal device memory path

Using Delphi XE8 on Android device Samsung S4