curl --request POST \
  --url https://api.shoppex.io/dev/v1/subscriptions/{id}/refund \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "reason": "Customer requested refund after duplicate charge."
}
'

{
  "data": {
    "message": "Refund applied to balance."
  }
}