GET /v1/billing/subscription
curl -X GET "https://api.whizo.ai/v1/billing/subscription" -H "Authorization: Bearer YOUR_API_KEY"
POST /v1/billing/checkout
curl -X POST "https://api.whizo.ai/v1/billing/checkout" -H "Authorization: Bearer YOUR_API_KEY" -H "Content-Type: application/json" -d '{ "plan": "pro", "billingPeriod": "monthly" }'