API "Unauthorized request." Error 1007 from any call

API "Unauthorized request." Error 1007 from any call

Hi,
I am using following python code to integrate listsubscribe endpoint of List Management API ( https://www.zoho.com/campaigns/help/developers/contact-subscribe.html) using v1.1

listKey = "f2************"
data = {
    "resfmt" : "JSON",
    "listkey" : listKey,
    "contactinfo" : {
        "First Name": "aaa",
        "Last Name": "bbb",
        "Contact Email": " abc@abc.com"
    },
    "sources" : "comingsoon"
}

r = requests.post(url, json=data);

The response I am getting following 

<?xml version="1.0" encoding="UTF-8" standalone="no"?><response
uri="/api/v1.1/json/listsubscribe" version="1"><code>1007</code><status>error</status><message>Unauthorized request.</message></response>