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e-Invoicing Document Interchange API Specification

The Public REST API provides programmatic access to an e-invoicing platform operated by a certified service provider, enabling companies to securely send, receive, and manage electronic invoices and related business documents via automated document interchange.

This OpenAPI-based specification describes all available endpoints for integrating your ERP or other business applications with the service provider’s platform, including onboarding, invoice submission, status tracking, document retrieval, and reporting.

To use the API, you must obtain access credentials from your chosen service provider.

Generating client libraries

You can generate strongly typed client libraries for various programming languages using the provided openapi.yaml file and the OpenAPI Generator.

  1. Download the openapi.yaml (or openapi.json) file from this site.
  2. Install the OpenAPI Generator following the instructions on the project website.
  3. Run the generator for your preferred language. For example, to generate a Java client:
   openapi-generator-cli generate \
     -i openapi.yaml \
     -g java \
     -o ./einvoice-java-client

Replace java with the desired generator (for example: typescript-axios, csharp, python) and adjust the output directory as needed.

Note for integration partners

If you are an integration partner, you need to obtain a softwareID that has to be included in request header on some API requests.

Here is an example

curl -i -X POST \
  https://omnizon-public-api--docs.preview.redocly.app/_mock/openapi/rest/v1/documents/send \
  -H 'Content-Type: application/octet-stream' \
  -H 'companyVatNumber: HR12345678910' \
  -H 'fiscalization: true' \
  -H 'x-fileName: string' \
  -H 'x-software-id: string' \  ##### Here goes your softwareID
  -d '<Invoice xmlns="urn:oasis:names:specification:ubl:schema:xsd:Invoice-2">...</Invoice>'

softwareID is necessary in the following API requests:

  • documents/send
  • documents/get

For non-integration partners softwareID is NOT required.

Change log

Current version 2026.07.01 as of 14.5.2026

  • Extended /documents/paid response with internalRequestId property.
  • Extended /documents/getAllReportingStatuses request with optional internalRequestId filter property.
  • Resolved calculation inconsistency issue in /billing/monthly-usage endpoint
  • Added AS4 error message to /documents/getStatus response when available.

Version 2026.05.02 as of 1.4.2026

  • fixed paging when documents do not have time component in timestamps in /inbox, /inbox/status, outbox/status
  • optimized /inbox performance
  • added AS4 delivery information in outbox/status i getStatus

Version 2026.03.01 as of 9.2.2026

  • added /getPdf - return PDF version of a document
  • added filtering and sorting options in inbox/status and outbox/status

Version 2025.09.05 as of 16.01.2026

  • Methods getStatus and getInternalStatus return a new field internalStatusDetails containing error messages with timestamp.

Version 2025.09.04 as of 31.12.2025

  • No breaking changes
  • Major change - introduction of (optional) paging on endpoints returning lists of documents
  • Additional document fields in /inbox, /inbox/status, outbox/status and getStatus
 

Document status