Here is a python request that I know works. Just replace the placeholders
import requests url = 'https://api2.westfax.com/REST/Fax_SendFax/JSON' payload = {'Username': 'Email@email.com', 'Password': 'password', 'Cookies': 'false', 'ProductId': '0000000-0000-0000-0000-000000000', 'JobName': ‘Patient Results #039239230’, 'Header': ‘Results for XYZ’, 'BillingCode': 'Patient #039239230', 'Numbers1': '9702895979', 'CSID': '(970) 289-5979', 'ANI': '9702895979', 'StartDate': '1/1/2020', 'FaxQuality': 'Fine', 'FeedbackEmail': 'doug@xnegenx.com'} files = {'Files0': open('TEST.pdf','rb')} headers = { 'ContentType': 'multipart/form-data' } response = requests.request('POST', url, headers = headers, data =payload, files = files, allow_redirects=False) print(response.text)