Rasa core returning 500 for custom action, request fired from rasa-ui

[kdigumar]

@paschmann ,hi and thanks for this UI which made things very simple.

I am facing below issue.
i have rasa-ui, rasa nlu, rasa-core in 3 different pods.
For one of my agent i have enabled rasa-core and created actions, intents, entities, stories and rasa core server is up and running with creates stories.
In dialogue flow i am calling custom action webhook url, this webhook url is an external api where its pod is up and url returning response.
But when rasa-core calling the same it is giving 500 error.
not sure if i am missing anything. can you please share your thoughts. PFB logs of core.

logs:

10.129.2.1 - - [2019-11-15 13:03:22] "POST /webhooks/rest/webhook HTTP/1.1" 200 619 0.270837

  | 2019-11-15 13:03:35 DEBUG rasa_core.tracker_store - Recreating tracker for id '1573822996031'
  | 2019-11-15 13:03:35 DEBUG rasa_core.processor - Received user message 'INC13693613' with intent '{'name': 'incident', 'confidence': 0.984804223228072}' and entities '[{'entity': 'ticket', 'value': 'INC13693613', 'start': 0, 'end': 11, 'confidence': None, 'extractor': 'MitieEntityExtractor'}]'
  | 2019-11-15 13:03:35 DEBUG rasa_core.processor - Logged UserUtterance - tracker now has 9 events
  | 2019-11-15 13:03:35 DEBUG rasa_core.processor - Current slot values:
  | happy_entity: None
  | ticket: INC13693613
  | unhappy_entity: None
  | 2019-11-15 13:03:35 DEBUG rasa_core.policies.memoization - Current tracker state [{}, {'prev_action_listen': 1.0, 'intent_greet': 1.0}, {'intent_greet': 1.0, 'prev_utter_greet': 1.0}, {'intent_greet': 1.0, 'prev_utter_how_to_help': 1.0}, {'prev_action_listen': 1.0, 'entity_ticket': 1.0, 'slot_ticket_0': 1.0, 'intent_incident': 1.0}]
  | 2019-11-15 13:03:35 DEBUG rasa_core.policies.memoization - There is a memorised next action '17'
  | 2019-11-15 13:03:35 DEBUG rasa_core.policies.form_policy - There is no active form
  | 2019-11-15 13:03:35 DEBUG rasa_core.policies.ensemble - Predicted next action using policy_2_MemoizationPolicy
  | 2019-11-15 13:03:35 DEBUG rasa_core.processor - Predicted next action 'action_webhook_ticket' with prob 1.00.
  | 2019-11-15 13:03:35 DEBUG rasa_core.actions.action - Calling action endpoint to run action 'action_webhook_ticket'.
  | 2019-11-15 13:03:35 ERROR rasa_core.actions.action - Failed to run custom action 'action_webhook_ticket'. Action server responded with a non 200 status code of 500. Make sure your action server properly runs actions and returns a 200 once the action is executed. Error: 500 Server Error: for url: http://rasa-chatbot-api-edi-b2b-chatbot-test.ocp-ctc-dmz-nonprod.optum.com/rasa/api/
  | 2019-11-15 13:03:35 ERROR rasa_core.processor - Encountered an exception while running action 'action_webhook_ticket'. Bot will continue, but the actions events are lost. Make sure to fix the exception in your custom code.
  | 2019-11-15 13:03:35 DEBUG rasa_core.processor - Failed to execute custom action