null if you have not created one yet (use POST /api/referral/create). Rate limit: 30 requests/min per account, separate from the POST budget.curl --location 'https://tunnelsats.com/api/referral/create' \
--header 'Accept;' \
--header 'Authorization: Bearer <token>'{
"code": "REF-7K2Q9Z",
"created_at": "2026-01-15 09:30:00",
"usage_count": 3
}