Connecting Your Croatian ERP to Peppol: A Technical Integration Guide

POST /invoices — Submit an Invoice

Send your invoice data as JSON to the API endpoint. InvoStaq's API accepts a simplified JSON payload (you don't need to construct UBL XML yourself) and handles the mapping to BIS 3.0 format. Include sender/receiver OIB, line items, VAT breakdown, and payment reference.

Automatic Validation

The API runs 200+ validation rules against your invoice data before converting to UBL. Croatian-specific validations include OIB checksum verification, VAT rate validation (25%/13%/5%/0%), required fields for CTC reporting, and business rule checks for credit note references.

Peppol Routing & Delivery

Once validated, InvoStaq routes your invoice through the Peppol network to the recipient's Access Point, identified by their Peppol Participant ID (typically their OIB). You receive a delivery receipt webhook confirming successful transmission.

CTC Reporting to Porezna Uprava

Simultaneously, the API reports the invoice to Croatia's tax authority endpoint for CTC processing. You don't need to implement a separate connection to the tax authority — the API handles this automatically.

Archiving & Retrieval

All invoices are automatically archived in UBL format for 11 years. The GET /invoices/{id} endpoint lets you retrieve any historical invoice, including its original XML, delivery receipts, and tax authority acknowledgment.

Use InvoStaq's test sandbox to submit invoices without reaching the live Peppol network or tax authority. Validate your JSON payloads, check UBL output, and verify all Croatian fields are correctly mapped.

Send test invoices through the Peppol test network to verify end-to-end delivery. Confirm that your trading partners' test environments receive the invoices correctly and that the response (MDN) comes back.

Verify that the CTC report to the Porezna Uprava test endpoint is generated correctly. Check that the tax authority acknowledgment is received and logged.

Deliberately send invoices with common errors (wrong OIB, missing VAT code, invalid payment reference) to verify your error handling. Ensure your ERP receives clear error messages and can display them to users.

If you process more than 100 invoices per day, run a volume test at 2x your expected peak. Check for rate limiting, timeout handling, and that your ERP's batch processing correctly handles Peppol responses.

Switch from test to production API credentials. Send your first live invoice and verify delivery. Monitor the first 24 hours closely, checking delivery receipts, CTC confirmations, and any validation warnings.

Set up dashboards to track delivery success rate, average processing time, rejection reasons, and CTC submission status. InvoStaq's dashboard provides this out of the box for Croatian compliance.