Change plan tier or billing interval (proration is config-driven)

curl -X PATCH https://api.moonborn.co/v1/billing/subscription \
  -H "Authorization: Bearer $MOONBORN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
      "planTier": "free"
    }'

import Moonborn from '@moonborn/sdk';

const client = new Moonborn({ apiKey: process.env.MOONBORN_API_KEY });

const result = await client.billing.changeSubscriptionPlan({
  planTier: "free",
});

import os
from moonborn import Moonborn

client = Moonborn(api_key=os.environ["MOONBORN_API_KEY"])

result = client.billing.change_subscription_plan(
    plan_tier="free",
)