https://lc-api.sdl.com/file-translations API - can't get it to work

I have successfully done a cloud api translation using the text translate service lc-api.sdl.com/translate but am unable to use the similar lc-api.sdl.com/file-translations API.

Can someone help or provide some sample python code?

This is the python code I am working with:

-----
import requests
filename='c:\\tmp\\em_si_mesmo.txt'
url = 'lc-api.sdl.com/file-translations'
headers = {'content-type': 'multipart/form-data',
'Authorization': <my-key>}

data={"from":"por",
"to":"eng"}

r = requests.post(url,
data=data,
files={'file': open(filename, 'rb')},
headers=headers)
print(r.text,end='\n')
-----

This is what I get back from the server

{ "errorCode": "GENERIC_APPLICATION_EXCEPTION", "message": "An error occured while processing your request!", "details": null }