Evaluate stories

I try to follow the guidance from “HTTP API”, My request is :

curl -XPOST http://localhost:5005/model/test/stories?token=12345678 -d "## happy path\n* greet\n\n  - utter_greet\n\n* mood_great\n\n  - utter_happy\n\n## sad path 1\n* greet\n\n  - utter_greet\n\n* mood_unhappy\n\n  - utter_cheer_up\n\n  - utter_did_that_help\n\n* affirm\n\n  - utter_happy\n\n## sad path 2\n* greet\n\n  - utter_greet\n\n* mood_unhappy\n\n  - utter_cheer_up\n\n  - utter_did_that_help\n\n* deny\n\n  - utter_goodbye\n\n## say goodbye\n* goodbye\n\n  - utter_goodbye"

the response is:

{"version":"1.5.3","status":"failure","message":"An unexpected error occurred during evaluation. Error: division by zero","reason":"TestingError","details":{},"help":null,"code":500}

How to evaluate stories? Could someone give me an whole example? Thanks a lot!