Ionic3 file transfer plugin cors error

I am using file transfer plugin but anytime i trigger the download i get cors error and i have settled every cors error in my backend. To be sure of this i copied an image url online and i tried downloading the image but i still get cors error which means its a problem from ionic not my backend.
And also i will like to ask that “how do you test the file transfer” because i run the command “ionic cordova run browser” to be able to test the plugin but i am not sure thats the right way maybe thats why I am having the cors issue… Please help me.