In many companies there is a gap between Projectile and accounting: invoices are created in the ERP, posted in DATEV, and in between files get exported, imported and fixed by hand. The interface I specified and saw through to production as a Projectile partner replaces that detour with a fully automated, bidirectional synchronization via the DATEV Desktop API and REST.
The solution is documented in a freely available 9-page whitepaper: not a marketing brochure, but technical documentation at the level that goes to development teams and tax advisors.
What the interface transfers
| Module | Direction | Mechanics |
|---|---|---|
| Outgoing invoices | Projectile → DATEV | Real-time transfer of posting batches; account assignment via a configurable Buchungsmatrix, a four-dimensional posting matrix (recipient country, invoice type, tax rate, cost type) |
| Incoming invoices | DATEV → Projectile | Scheduled synchronization of finalized posting batches with automatic document creation |
| Debtors & creditors | Projectile → DATEV | Event-driven master data synchronization with client assignment |
| Document images | Projectile → DATEV DUO | Automatic XML/ZIP packages, audit-proof and GoBD-compliant |
Edge cases and operations
The standard case is quickly explained; the substance sits in the exceptions. Advance invoices, installment invoices and cancellations are specified as scenarios of their own, including the posting logic behind them. Errors do not disappear silently: configurable notifications and manual retry actions let accounting see what is stuck and intervene. The configuration is multi-client capable, and each module can be activated per DATEV client individually.
E-invoicing raises the stakes
Since January 1, 2025, German companies must be able to receive e-invoices. From January 1, 2027, issuing becomes mandatory for companies with prior-year revenue above 800,000 euros, and from 2028 for everyone. An automated path from document to finalized posting batch is no longer a convenience: it is what keeps XRechnung and ZUGFeRD from ending in manual rework. How I approach this beyond Projectile is covered under E-Invoicing & DATEV; the e-invoicing middleware for it is currently in development, with a demo appointment on request.