curl -X POST https://identity-sandbox.payven.com.tr/api/v1/auth/8e3f5c12-9a7b-4c8d-bc4e-2c963f66afa6/token \
  -H "Authorization: Bearer $PAYVEN_TOKEN" \
  -H "Idempotency-Key: order-1001" \
  -d '{ ...payload... }'

{
  "access_token": "<string>",
  "refresh_token": "<string>",
  "expires_in": 123,
  "refresh_expires_in": 123,
  "token_type": "<string>",
  "scope": "<string>"
}