Module: Billing

Plans, subscriptions, usage metering, monthly invoicing. Manual payment marking — no payment provider. Module Order = 500.

Entities / DbContext: BillingPlan, Subscription, Invoice (+ InvoiceLineItem), UsageSnapshot. BillingDbContext : DbContext (NOT BaseDbContext) — billing lives in the main DB with an explicit TenantId column for cross-tenant admin visibility, filtered in query services. Contracts = DTOs; IBillingService/IUsageReporter are internal. Areas: Plans, Subscriptions, Invoices (generate/issue/mark-paid/void), Usage (capture/get). Monthly invoice job (5 0 1 * *). Full list: Features/v1/ or /scalar.

Gotchas

• BillingPlan is IGlobalEntity — platform-wide catalogue rows, not tenant-scoped (opts out of tenant isolation). A plan's Key matches the quota config key (e.g. "pro"): limits come from QuotaOptions, prices/overage from the plan.
• BillingDbContext is a plain DbContext — tenant filtering is done explicitly in query services, not by the BaseDbContext auto-filter. Don't assume the global tenant filter applies here.
• Invoice state machine — Draft → Issued → Paid | Void. Line items only addable in Draft; a Paid invoice can't be voided; totals recompute on add; Issue defaults due = +14 days.
• Usage metering is idempotent — IUsageReporter.CaptureForPeriodAsync reads IQuotaService and persists one UsageSnapshot per QuotaResource per (tenant, period), so invoicing math is reproducible even after a mid-period plan change.