VARIABLE IS NOT DEFINED ! response from API Call in Ansible

The following is my playbook containing a Rest Call

---
-
 name: "REST CALL"
 hosts: local
 tasks:
    - name: "REST Call to Get Session ID"
      uri:
        url: http://192.168.96.172:5300/avxapi/acctmgmt-perform-login?gwkey=f000ca01&gwsource=web
        method: POST
        body: "{{ lookup('file','empty.json') }}"
        body_format: json
        return_content: yes
        headers:
          Content-Type: "application/json"
          username: "admin"
          password: "Apptest@123"
      register: login

    - debug:
        var: "{{ login }}"

And this is my response

PLAY [REST CALL] *********************************

TASK [Gathering Facts] *********************************************************
ok: [localhost]

TASK [REST Call to Get Session ID] *********************************************
ok: [localhost]

TASK [debug] *******************************************************************
ok: [localhost] => {
    "<type 'dict'>": "VARIABLE IS NOT DEFINED!"
}

Can anybody find why I'm not getting a proper response? And btw, the body just contains an empty payload. The empty.json looks like this

{"payload":{}}