E-Invoicing with Open Mercato: Streamline Invoice Workflows up to 5x Faster

As technology advances, expectations rise. Business teams need digital solutions that do more than automate routine tasks. They expect technology to accelerate complex processes and deliver measurable savings sooner. That is why we chose Open Mercato, an open-source, AI-native framework designed to speed up the development and continuous improvement of business applications tailored to each organization.

GoNextStage brought the proven logic of its KSeF Connector to Open Mercato. The solution had already been deployed in WEBCON and as a standalone application, so the project started with validated business logic, hands-on back-office automation experience, and ready-to-use PBM process blueprints. The results came quickly.

Built on Open Mercato, the GoNextStage KSeF Connector comes with integration, scheduling, event handling, access control, and workflow capabilities out of the box. It can be configured around the way a company’s accounting team actually works, including its organizational structure, user roles, approval paths, consultations, exceptions, and document routing rules.

Most importantly, we delivered the first version of the application, integrated with the purchase-to-pay and invoice workflow, 5 times faster than with traditional software development. For clients, this means the first improvements to e-invoice processing can go live within 14 days of development starting.

How the GoNextStage e-Invoicing Connector works

Poland

In the case of Polish National e-Invocing System (KSeF), invoices are retrieved from KSeF, matched to the appropriate legal entity using tax identification data, saved with key metadata, and routed into the workflow. We designed the import mechanism to withstand errors and temporary KSeF downtime, including offline-mode scenarios. If synchronization with KSeF needs to be restarted, processing can resume without creating duplicate invoices.

KSeF authentication is handled at the organization level. The application’s access to KSeF only needs to be authorized once; individual user permissions are then managed in the KSeF Connector application on Open Mercato. Role-based document access is especially important in multi-entity environments, where users should only see the invoices they are authorized to view.

After import, each invoice follows a workflow tailored to the client’s operating model. Depending on the process, this may include registration, coding and business details, approval, accounting review, consultation, and archiving.

For Polish e-invoices, an intuitive interface was essential. Instead of working with raw XML files, users see a clear, readable invoice, making the process easier for both accounting teams and business approvers. They can also flag invoices that require attention, export invoice data to a table, and manage KSeF attachments.

Hungary

NAV is Hungary’s real-time invoice reporting system. Unlike Poland, Hungary does not operate a KSeF-style platform for exchanging invoices between businesses. The main compliance risk is failing to report a transaction to NAV, or reporting it late. Penalties can reach HUF 500,000 per unreported invoice, so even a few dozen missed reports a month can cost far more than implementing an automated integration.

Purchase invoice validation introduces another layer of risk. Mismatches between a company’s accounting records and the data submitted to NAV can trigger an audit, create inconsistencies in tax reporting, and—when accompanied by other irregularities—prompt the tax authorities to question the company’s returns. GoNextStage’s e-invoicing solution for Hungary helps companies mitigate these risks.