curl --request POST \
  --url https://sandbox.withclasp.com/plan_configurations \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "plan": "<string>",
  "waiting_period": {
    "policy": "end_of_waiting_period",
    "period": "day",
    "duration": 123
  },
  "required_subclass": "<string>"
}'

{
  "id": "<string>",
  "plan": "<string>",
  "termination_policy": "termination_date",
  "waiting_period": {
    "policy": "end_of_waiting_period",
    "period": "day",
    "duration": 123
  },
  "required_subclass": "<string>"
}