Many businesses, one platform
Accountants work across dozens of client companies. Each company’s financial data must be strictly isolated from every other.
Case study · Financial services · Live platform
A compliance-first accounting and e-invoicing platform engineered for a national tax mandate.
A multi-tenant platform giving regulated small businesses and their accountants one system for books, tax returns and mandatory electronic invoicing, with the audit trail regulators expect.
- 35
- domain modules in one platform
- 2
- layers of tenant isolation, application and database
- 0
- records lost in the one production incident, which became a migration rule
- EN · AR
- bilingual with right-to-left support
Governments are moving to mandatory electronic invoicing, where every invoice is exchanged in a structured format through accredited networks and reported to the tax authority. For small businesses, this turns bookkeeping from an internal task into a regulated process.
Watin was built for that shift: a single platform in which the business owner keeps the books and the accountant works across many clients, with compliance designed into the data model rather than added afterwards.
The challenge
What made it hard.
Records that must not change
Tax records need a trail that shows exactly who did what and when, and that cannot be quietly edited or deleted.
Network-grade e-invoicing
Mandatory e-invoicing requires exchanging documents over the Peppol network using its AS4 messaging protocol.
Exact money
Rounding errors that are tolerable in most software are unacceptable in tax returns.
Our approach
How we solved it.
- 01
Isolation enforced twice
Tenant separation is enforced in the application and again by row-level security in the PostgreSQL database, with an automated sweep that checks every table.
- 02
Append-only audit trail
The audit log cannot be edited or truncated, and the accounting practice tier uses a hash-chained event log to make tampering evident.
- 03
In-house Peppol access point
Rather than depend on a reseller, the team built its own AS4 access-point service, integration-ready ahead of network accreditation.
- 04
A gate before every change
Lint, type checks, dependency and dead-code analysis, security audits, three test lanes, browser journeys and rehearsed database migrations run before code reaches production.
Highlights
Also delivered.
- Embedded AI assistant built on a large language model, plus OCR extraction of supplier documents
- Money handled in exact decimal and minor-unit arithmetic throughout
- Database migrations rehearsed on a disposable stack in CI before they touch production
- A production schema drift was caught, fixed without data loss and turned into a standing rule: migrations must be additive and backward-compatible
Technology
The stack.
- Next.js
- TypeScript
- PostgreSQL
- Row-level security
- Java (AS4)
- Peppol
- Playwright
- Sentry
What comes next
Live e-invoicing exchange follows network accreditation of the access point, which is a regulatory step rather than an engineering one.
Hurbad, Watin, TravelOS and CaafimaadAI are platforms built and operated by the Resolv team as our own ventures. We publish them because they are the clearest evidence of how we work: the same people, standards and methods we bring to client engagements.
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