curl --request POST \
  --url https://api.steppay.kr/api/v1/subscriptions/{subscriptionId}/change-pay-datetime \
  --header 'Content-Type: application/json' \
  --header 'Secret-Token: <api-key>' \
  --data '
{
  "when": "2023-11-07T05:31:56Z"
}
'

{
  "message": "<string>",
  "body": {}
}