Centralized billing engine that makes this Odoo 19 Enterprise instance the single billing brain for every NexaSystems service — NexaCloud hosting, NexaDesk chat, NexaMaps API, custom apps, and memberships. It replaces Lago and absorbs NexaCloud's home-grown Stripe billing into one customer ledger and one accounting system.

Design spec: docs/superpowers/specs/2026-05-27-nexa-billing-centralized-design.md

Status: SCAFFOLD. Models + security + the API auth shell are in place and the module installs. The usage engine, full inbound API, and webhook processor are stubs to be implemented from the writing-plans output.

Why this module is small

We build only the metering + integration layer. Everything financial — recurring invoicing, HST tax, proration, dunning, customer portal, credit notes, Stripe — is native Odoo Enterprise (sale_subscription, account_accountant, payment_stripe), already installed and running.

Design decisions (locked)

Odoo fully replaces Lago (we build the metered-billing engine; Lago is decommissioned last).
One unified res.partner per client; separate invoice per service.
Apps drive, Odoo is the billing system of record — apps call the inbound API (as they call Lago today); Odoo bills and webhooks back.
Odoo owns the billing catalog; apps own feature entitlements (shared plan_code).
Pilot = NexaCloud, phased dual-run cutover.
Aggregate-push usage ingestion (periodic counters, not a raw-event firehose).

Models (`fusion.billing.*`)

Model	Purpose
`fusion.billing.service`	One source app; bearer API key (hashed) + webhook config.
`fusion.billing.account.link`	External account id → one `res.partner` (identity resolution).
`fusion.billing.metric`	Billable metric + aggregation (sum/max/last/unique).
`fusion.billing.charge`	Plan + metric → included quota + overage pricing.
`fusion.billing.usage`	Aggregated per-period usage rollups (idempotent).
`fusion.billing.webhook`	Outbound lifecycle event queue (HMAC + retry).
`fusion.billing.reconciliation`	Dual-run Odoo-vs-app delta during cutover.

Odoo 19 note (verified): a subscription is a sale.order with is_subscription=True (plan_id → sale.subscription.plan). There is no sale.subscription model. fusion.billing.usage.subscription_id therefore points at sale.order.

Inbound API

Lago-shaped REST under /api/billing/v1/*, bearer auth. Endpoints mirror NexaDesk's existing lago-client.ts so migration is a thin client swap. /health works today; the rest return 501 until implemented.

Relationship to `fusion_api`

fusion_api manages outbound provider keys (OpenAI, Maps, Twilio) + cost tracking — i.e. COGS. This module tracks customer revenue. Complementary: feed fusion_api cost into margin reporting; reuse its daily-rollup aggregation pattern.

Dependencies

account_accountant, sale_subscription, sale_management, payment_stripe.

Local dev

docker exec odoo-nexa-app odoo -d nexamain -u fusion_centralize_billing --stop-after-init
# tests (once added):
docker exec odoo-nexa-app odoo -d nexamain --test-enable --test-tags /fusion_centralize_billing -u fusion_centralize_billing --stop-after-init

Canadian English, CAD, HST via account.tax. New fields on native models use the x_fc_* prefix.

README.md

Fusion Centralized Billing (fusion_centralize_billing)