# Bookkeeping Data

This example case describes how to use the API to sync bookkeeping data (verifications, transactions) to an external system.

## Sections

- [Activation level](/introduction/cases/bookkeeping-data/activation-level) — Choose per-company or per-organization credentials.
- [Access](/introduction/cases/bookkeeping-data/access) — Required entities and permissions.
- [Implementation example](/introduction/cases/bookkeeping-data/implementation-example) — Step-by-step data fetching and optional sync marking.


## Entity relationships

Verifications are created from Invoice, Payment, or Debt Invoice events; that determines whether a verification is linked to an Invoice, Payment, or Debt Invoice.

**Bookkeeping chain:**

```mermaid
flowchart TB
  C[Company]
  VG[Verification Group]
  V[Verification]
  T[Transaction]

  VG --> C
  V --> VG
  T --> V
```

**Verification sources and invoice PDFs:**

```mermaid
flowchart TB
  V[Verification]
  I[Invoice]
  P[Payment]
  DI[Debt Invoice]
  PDF[Invoice Related PDF File]

  V --> I
  V --> P
  V --> DI
  PDF --> I
```