Twilio Integration not working

I have been trying to integrate WhatsApp notifications using Twilio. I have been following the steps as per this video Understanding How to Integrate Twilio with ERPNext - YouTube. Whenever I try to open Twilio Settings from the integration page, it shows an error “DocType Communication Medium not found” & “The resource you are looking for is not available”.

I have installed the twilio integration and have setup a notification alert on submission of Sales order. But the notification does not succeed and it shows this error.

Traceback (most recent call last):
  File "/home/aaron/frappe-bench/apps/frappe/frappe/email/doctype/notification/", line 137, in send
    self.create_system_notification(doc, context)
  File "/home/aaron/frappe-bench/apps/frappe/frappe/email/doctype/notification/", line 168, in create_system_notification
    if "{" in subject:
TypeError: argument of type 'NoneType' is not iterable

Am not sure what does this error mean and how to correct it.
Please help!!!