Pigeon library timeout error

Hi,
I have pigeon configured and I have obtained the certificates as mentioned in the documentation by converting key.12 and cert.12 into key.pem and cert.pem on a command line. But when I try to test the notification on the console. I am getting these logs and then the response is timeout. It’s my first time playing with push notifications.

 00:40:15.086 function=decode/3 module=ssl_alert [info] TLS :client: In state :cipher received 
 SERVER ALERT: Fatal - Unknown CA

 00:40:16.062 function=decode/3 module=ssl_alert [info] TLS :client: In state :cipher received 
 SERVER ALERT: Fatal - Unknown CA

 00:40:17.150 function=decode/3 module=ssl_alert [info] TLS :client: In state :cipher received 
 SERVER ALERT: Fatal - Unknown CA


    %Pigeon.APNS.Notification{
      collapse_id: nil,
      device_token: 
      "83a1497681c2e9",
      expiration: nil,
      id: nil,
      payload: %{"aps" => %{"alert" => "testing push notification"}},
      priority: nil,
      push_type: "alert",
      response: :timeout,
      topic: "topic_name"
     }

Pigeon version is 0.14 and the configuration is below:
It’s a umbrella application and these settings are present in the root config file.

config :pigeon, :apns,
apns_default: %{
  cert: "priv/certs/cert.pem",
  key: "priv/certs/key_unencrypted.pem",
  mode: :dev
}

Any help will be much appreciaated.
Thank you