Twilio : Make a call using Connect App | Twilio.Device Error: ConnectionError (53000)

Question

I am trying to make a call using Twilio Connected App. I have

1. Registered a new connect app
2. Authorized the connect(step 1) with my account
3. Bought/provisioned a new incoming phone number using connected app (step 1).

Using python helper library, I am trying to call a number. But i keep getting error [ Twilio.Device Error: ConnectionError (53000) ].

    # sid issued by Twilio when we authorised the connect app
    account_SID = request.user.organization.twilio_sid 

    # env.Twilio_SID is my API key (main) SID and env.TWILIO_SECRET is secret of the same API key
    # identity is phone number that we provisioned using the connected app
    access_token = AccessToken(account_SID,env.TWILIO_SID, env.TWILIO_SECRET, identity="+17208****")

If I replace the account_SID with my parent account SID, the access token works. But if I use SID related to connected app, it throws this error.

What can i change to make it work?