curl --request POST \
  --url https://api.staging.kathan.tech/credits/redeem-promo \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --header 'X-User-ID: <api-key>' \
  --data '
{
  "code": "<string>"
}
'

{
  "credits_granted": 123,
  "new_balance": 123
}