curl --request POST \
  --url https://{operatorDomain}/v1/admin/notifications/reminder-rules/{id}/stages \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "id": "nstg_01h...",
  "ruleId": "<string>",
  "offsetDays": 123,
  "position": 123,
  "channels": [
    {}
  ]
}
'

{
  "id": "nstg_01h...",
  "ruleId": "<string>",
  "offsetDays": 123,
  "position": 123,
  "channels": [
    {}
  ]
}