curl --request POST \
  --url https://payments.oaknetwork.org/api/v1/subscription/plans \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "name": "Monthly Pro",
  "description": "Monthly professional plan",
  "frequency": 30,
  "price": 2999,
  "currency": "USD",
  "created_by": "admin@example.com"
}
'

{
  "msg": "plan created",
  "data": "<string>"
}