Don't understand INVALID_REQUEST_METHOD when I try to post up an attachment

Don't understand INVALID_REQUEST_METHOD when I try to post up an attachment

When I make the POST request (using python requests.post() for files):
I get this response:
  1. r:{
  2.   "code": "INVALID_REQUEST_METHOD",
  3.   "details": {},
  4.   "message": "The http request method type is not a valid one",
  5.   "status": "error"
  6. }
  7. requests.exceptions.HTTPError: 400 Client Error:  for url: https://www.zohoapis.com/crm/v8/Calls/*********************01/Attachments

The "files" parameter is
  1. files={"attachmentUrl": link}

Please advise on how I can fix this error.

Thanks
Clark