Accountable for Independents API & PEPPOL Integration

Invoice & quote API

Read and write invoices and quotes with full line-item detail, VAT code, customer reference and payment status. Useful for migrating an existing client base into Accountable, or re-using Accountable invoices inside a custom CRM. Recurring-invoice templates and duplicate-invoice flows are mapped to predictable REST endpoints.

PEPPOL access-point bridge

Since Accountable is a certified PEPPOL access point and PEPPOL became mandatory for Belgian B2B invoicing in January 2026, this module mirrors the outbound flow: it converts your ERP invoice into UBL 2.1, validates against the BIS Billing 3.0 schema, and submits via the same network the user is already onboarded to.

VAT & income-tax export

Pulls the periodic VAT declaration (BE) or USt-VA (DE) and the annual income-tax / EÜR figures the app generates. The module also exposes the AI Assistant's tax-tip metadata per expense, so accountants can audit which deductions were suggested by AI.

Receipt OCR & expense feed

Streams scanned receipts with the OCR text, the AI-suggested expense category, the matched bank transaction and the tax-deductibility verdict. Practical for expense-management dashboards or factoring partners that need confirmed proof-of-spend.

PSD2 bank-feed mirror

Mirrors the Account Information Service (AIS) feed Accountable maintains under its Belgian PSD2 license. Returns transactions, balances and the "set aside for taxes" figure that the app shows in real time, so a third-party fintech can build the same reserve view inside its own product.

Accountant collaboration export

Bundles invoices, receipts, VAT returns and tax filings into a structured archive that an accountant or auditor can ingest. Mirrors the in-app "share with my accountant" flow but as a programmatic deliverable — useful for accounting platforms that want to onboard Accountable customers without manual exports.

1. Embedded business banking partner

Context: a neobank or business banking provider (similar to the Swan partnership Accountable already runs) wants to surface tax-reserve and VAT figures inside its own app. Data: PSD2 transactions, VAT period totals, tax-reserve percentage. OpenData angle: a one-way OpenBanking AIS feed plus a side channel for Accountable's pre-computed tax-reserve recommendation, so the bank does not need to rebuild the calculator.

2. ERP / CRM invoice sync

Context: a freelancer using both an industry ERP and Accountable wants every quote that turns into a sale to flow into the app as an invoice. Data: invoice header, line items, VAT codes, customer record. OpenData angle: bidirectional sync where the ERP is the source of truth for billing while Accountable remains the source of truth for tax categorization and PEPPOL submission.

3. PEPPOL gateway for accountants

Context: an accounting firm onboarding 200 self-employed clients onto Accountable wants a single dashboard to monitor PEPPOL deliveries. Data: PEPPOL message status, UBL payloads, error codes, retries. OpenData angle: a multi-tenant view over many Accountable accounts, each with its own consent token, surfaced through one accountant-facing API.

4. Lending & underwriting feed

Context: a freelancer-focused lender wants to underwrite a credit line based on real revenue. Data: last 12 months of issued invoices, VAT returns and matched bank transactions. OpenData angle: a read-only OpenFinance bundle, snapshotted at decision time, signed and timestamped so the lender can defend the decision later.

5. ELSTER & INTERVAT compliance dashboard

Context: a tax-tech vendor consolidates VAT and income-tax submissions across Germany (ELSTER) and Belgium (INTERVAT). Data: declaration status, submission timestamp, official receipt. OpenData angle: the integration treats Accountable as the upstream filer and exposes a normalized status model that downstream compliance tools can poll.

1. Account login & token refresh

POST /api/v1/accountable/auth/login
Content-Type: application/json

{
  "email": "freelancer@example.eu",
  "password_or_otp": "<user-supplied>",
  "device_id": "of-lab-bridge-01"
}

200 OK
{
  "access_token": "eyJhbGciOi...",
  "refresh_token": "rt_8a2f...",
  "expires_in": 3600,
  "tenant": {
    "vat_number": "BE0123456789",
    "country": "BE",
    "language": "en"
  }
}

2. Invoice export with PEPPOL state

GET /api/v1/accountable/invoices?from=2026-01-01&to=2026-04-30
Authorization: Bearer <ACCESS_TOKEN>

200 OK
{
  "items": [
    {
      "invoice_id": "INV-2026-0142",
      "issued_at": "2026-04-12",
      "customer": {"name": "ACME SA", "vat": "BE0987654321"},
      "lines": [{"desc":"Consulting","qty":3,"unit_price":850.00,"vat_rate":21}],
      "total_excl_vat": 2550.00,
      "total_vat": 535.50,
      "peppol": {"status":"delivered","message_id":"a8d4...","ubl_version":"2.1"},
      "payment_status": "paid"
    }
  ],
  "next_cursor": null
}

3. PSD2 transaction webhook

POST https://your-app.example.com/webhooks/accountable/tx
X-Accountable-Signature: v1=8d6e...

{
  "event": "transaction.matched",
  "tenant_vat": "DE123456789",
  "tx": {
    "id": "tx_4f31",
    "iban": "DE89XXXX",
    "amount": -129.50,
    "currency": "EUR",
    "booked_at": "2026-04-29T08:14:00Z",
    "matched_receipt_id": "rcp_8821",
    "ai_category": "software_subscription",
    "deductible": true,
    "tax_reserve_advice_eur": 0
  }
}

Webhook signatures use HMAC-SHA256 over the raw body with a per-tenant secret. Failed deliveries follow an exponential-backoff retry policy capped at 24 hours, and replays are detected via the X-Accountable-Delivery-Id header.

Regulatory anchors

Accountable SA is authorised by the National Bank of Belgium and, in Germany, supervised by both the National Bank of Belgium and the Federal Financial Supervisory Authority (BaFin) under the revised Payment Services Directive (Directive (EU) 2015/2366, PSD2). Any AIS-style integration we build inherits those obligations: explicit user consent, strong customer authentication and a 90-day re-consent cadence.

Data-protection guardrails

Personal data flows are designed against the EU General Data Protection Regulation (GDPR): minimisation by default, encryption in transit and at rest, audit logs for every read, and configurable retention windows that match Belgian and German bookkeeping retention rules (typically 7 to 10 years for tax-relevant documents).

PEPPOL & e-invoicing rules

Outbound e-invoicing follows the PEPPOL BIS Billing 3.0 specification. Belgian B2B invoicing has been mandatory on PEPPOL since January 2026, and Germany's stepwise B2B e-invoicing rollout is already in flight, so each integration ships with schema validation and a digital-receipt store.

What you receive

• OpenAPI / Swagger specification of every endpoint we expose
• Protocol & auth-flow report (OAuth, token refresh, PSD2 SCA hooks)
• Runnable source for invoice export, PEPPOL bridge and PSD2 mirror in Python and Node.js
• Automated test suite with sandbox fixtures and replayable webhook payloads
• Compliance brief covering PSD2, GDPR and PEPPOL retention

Two engagement models

• Source code delivery from $300 — runnable API source code plus documentation, paid only after you confirm everything works on your side.
• Pay-per-call API billing — call our hosted endpoints and only pay per successful call, with no upfront commitment. Ideal for pilots and seasonal usage spikes such as quarterly VAT cycles.

Who we are

OpenFinance Lab is an independent technical studio focused on App interface integration and authorized API integration. Our engineers come from banking, payment gateways, mobile protocol analysis and cloud platforms, and we have shipped integrations across financial, e-commerce, hotel/travel and OTT app categories. For Accountable specifically, we lean on hands-on experience with PSD2 AIS feeds, PEPPOL access points and ELSTER-adjacent submission flows.

Contact

Tell us the target app, the data you want to read or write, and any deadlines you have. We typically respond within one business day with a scope confirmation and a fixed-price quote.

Open the contact page

Engagement workflow

1. Scope confirmation: which Accountable surface you need (invoices, PEPPOL, VAT, bank feed) and authorization model.
2. Protocol analysis and API design (2–5 business days, complexity-dependent).
3. Build and internal validation against sandbox and real test accounts (3–8 business days).
4. Documentation, sample code and test cases (1–2 business days).
5. First delivery typically lands in 5–15 business days; PEPPOL or multi-tenant accountant builds may extend the timeline.

FAQ

What do you need from me to start an Accountable integration?

How long does delivery take for an Accountable API drop?

How do you handle PSD2, GDPR and tax-data compliance?

Can the integration push e-invoices to PEPPOL on behalf of an Accountable user?