Subscription “drift” is when billing says one thing, your database says another, and the user experience becomes random: access revoked incorrectly, upgrades not applied, refunds not reflected, or seats miscounted. Fixing drift requires one principle: entitlements are a modeled system, not a flag.
Common Drift Patterns
- Upgrade/downgrade proration mismatches (provider vs internal state).
- Webhook ordering (invoice.paid arrives after subscription.updated).
- Retries that create duplicate “grant” operations.
- Refund/chargeback changes access incorrectly (or not at all).
The Entitlement Model (What to Store)
Model access as explicit grants with scope and validity window. Example primitives: plan, seats, features, limits, roles.
// Minimal entitlement record
entitlement {
accountId,
key: "feature.export" | "plan.pro" | "seats",
value: "true" | "10" | "pro",
source: "stripe" | "manual" | "promo",
validFrom,
validTo,
state: "ACTIVE" | "REVOKED",
correlationId
}Use a State Machine for Billing → Access
Providers are eventually consistent and webhooks are replayed. Convert provider events into a strict state machine. Your system should only allow safe transitions.
PENDING → ACTIVE → PAST_DUE → GRACE → SUSPENDED → CANCELED
↘ REFUNDED / CHARGEBACK (policy-dependent)Idempotency & Reconciliation (Non-Negotiable)
- Store raw events unique by event_id.
- Transform events into commands unique by correlationId.
- Apply grants/revokes idempotently (unique constraint per correlationId + entitlement key).
- Run a reconciliation job (hourly/daily) to heal rare gaps.
Seat-Based SaaS: The Right Way
Seats are an entitlement with a numeric limit. Enforce it centrally in authorization checks, not scattered across UI.
- Keep seat allocation separate from seat limit.
- Prevent race conditions with transactions or optimistic locking.
- Audit seat changes (who/when/why).
Security Angle: Entitlements Are Authorization
Drift can become a security defect: a user retains access after cancellation, or sees data they shouldn’t. Treat entitlements as part of your auth boundary: signed admin actions, audit logs, least privilege, and anomaly alerts.
Why This Converts
Search intent here is extremely high: “subscription access issues”, “webhooks out of order”, “entitlements model”. Companies with billing pain have budgets — and they want a team that can stabilize revenue without breaking UX.
