fix(billing): reset usage on transition from free -> paid plan

[waleedlatif1]

Summary

reset usage on transition from free -> paid plan, so if someone goes from free to pro plan, their usage restarts at 0, previously it would stay where it was

Type of Change

• Bug fix

Testing

N/A

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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Project	Deployment	Preview	Comments	Updated (UTC)
sim	Ready	Preview	Comment	Sep 22, 2025 8:55pm

1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
docs	Skipped			Sep 22, 2025 8:55pm

[greptile-apps]

Greptile Summary

This PR addresses a billing issue where users upgrading from free to paid plans would retain their accumulated usage statistics instead of starting fresh with their new subscription. The change implements a usage reset mechanism that triggers when users transition from free tier to paid plans (pro, team, or enterprise).

The implementation involves three key changes:

1. Exporting the usage reset function (apps/sim/lib/billing/webhooks/invoices.ts): Makes the existing resetUsageForSubscription function exportable so it can be reused across the billing system. This function moves current period costs to last period costs and sets current usage to 0.

2. Adding subscription creation handling (apps/sim/lib/auth.ts): Integrates a call to handleSubscriptionCreated in the onSubscriptionComplete hook to trigger usage reset when subscriptions are created through the authentication flow.

3. Creating the subscription webhook handler (apps/sim/lib/billing/webhooks/subscription.ts): Implements the core logic that detects free-to-paid transitions by checking if users have other active subscriptions. When a user with no previous active subscriptions creates a paid plan subscription, their usage gets reset.

This change integrates with the existing usage monitoring system documented in sim/lib/usage-monitor.ts, which tracks user usage against subscription limits and provides the UsageData interface used throughout the application. The reset ensures that paying customers get the full value of their subscription limits from day one rather than being penalized for free tier usage.

Confidence score: 4/5

• This PR addresses a legitimate billing fairness issue with a well-structured solution
• Score reflects solid implementation using existing patterns and proper error handling
• Pay close attention to the subscription webhook handler logic and database query conditions

_{3 files reviewed, 1 comment}

_{Edit Code Review Bot Settings | Greptile}

[icecrasher321]

it shouldn't be possible to have multiple active subscriptions tbh -- is this the case rn if I a pro user is added to a team?

[icecrasher321]

or is this something to do with cancelling paid subscriptions?