This endpoint is the second step in the onboarding process (and is continually used thereafter using polling mechanism)

1. After a session is created using the InitOnboarding endpoint and a token is generated.
2. Clients poll this endpoint with the token to retrieve the current step.
3. Depending on the response, the client may need to collect specific data or perform certain actions
   before calling Submit with that data.
   When the node type is externalData, inspect expectedFields to know exactly which payload fields must be submitted to submitUrl.
4. The client can then poll again to see if new steps are required or if the process has finished.
   Possible values are running, pending, failed or completed. Whenever pending is returned, the client should stop polling and submit the required payload according to the step type.