How to copy file using expo filesystem

I am trying to create a simple whatsapp status downloader app for android using expo and I am using expo-file-system for copying file but I am unable to get the file anywhere. My functions looks something like this :

export const saveFile = async (filePath) => {
const res = await FileSystem.copyAsync({
  from: filePath,
  to: `${FileSystem.documentDirectory}saved/test.mp4`,
});
};

where filepath uses SAF file path.