Starts validation or export of a task.
The task's state must be pending:start_client_action and its client_action must match the action parameter to make this request.
When a validation action is specified, the response contains a Validation Specification that contains all the information a client needs to display the task to a user for validation.
When an export action is specified, the response contains an Export Specification that contains all the information a client needs to export the data for the task.
After a successful request, the task's state is set to pending:complete_client_actionand a Complete Client Action request is expected to be received within the timeout period (30 minutes by default). A Cancel Client Action request or Fail Client action request can be made instead of Complete Client Action request.