curl --request POST \
  --url https://api.unibee.dev/merchant/subscription/change_due_day \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "dueDay": 123,
  "subscriptionId": "<string>"
}
'

{
  "code": 123,
  "data": {},
  "merchantId": 123,
  "message": "<string>",
  "redirect": "<string>",
  "requestId": "<string>"
}