curl -X POST "https://api.magpipe.ai/functions/v1/stripe-add-credits" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "amount": "50",
    "success_url": "https://yourapp.com/billing?success=true",
    "cancel_url": "https://yourapp.com/billing?canceled=true"
  }'

{
  "sessionId": "cs_live_a1b2c3d4e5f6g7h8i9j0",
  "url": "https://checkout.stripe.com/c/pay/cs_live_a1b2c3..."
}

{
  "error": "Invalid amount. Must be between 10 and 1000 or a preset value."
}