E-Invoicing in Accounting Software: Integration and Automation

Mandatory e-invoicing confronts businesses not only with the question of how to create and receive e-invoices, but also how to integrate them into their existing accounting workflows. An e-invoice only delivers real value when its structured data flows automatically into the accounting software rather than being retyped by hand. In this article, we show how successful integration works and the role API-based solutions play.

The Challenge: Accounting Software and E-Invoicing

Many businesses rely on established accounting solutions that have grown over the years. Support for structured e-invoicing formats such as XRechnung or ZUGFeRD varies widely:

• Some providers have already integrated native e-invoicing support
• Others offer it as a paid add-on module
• Some have no solution at all yet

As a result, many businesses can receive e-invoices but cannot process the data automatically. Instead, XML files are opened manually, read through, and the values are entered into the accounting system by hand. This is error-prone, time-consuming, and defeats the very purpose of e-invoicing.

Common Accounting Solutions in Germany

DATEV

DATEV is the de facto standard for collaboration between businesses and tax advisors in Germany. DATEV supports the import of e-invoices via the DATEV interface and the Unternehmen Online portal. ZUGFeRD invoices can be imported directly. For XRechnung in pure XML format, a conversion step or intermediate processing is often required.

lexoffice

lexoffice by Lexware is aimed at small businesses and freelancers. The software increasingly supports e-invoice imports and can process ZUGFeRD PDFs. Export functionality in the XRechnung format is also available, with the scope of features being continuously expanded.

sevDesk

sevDesk offers a cloud-based accounting solution with growing e-invoicing support. The platform can capture incoming invoices via OCR and is working toward full support for structured formats.

Sage and SAP

Larger ERP systems such as Sage and SAP typically have modules or partner integrations for e-invoicing. However, configuration is often complex and requires specialized expertise.

What Integration Actually Means

True e-invoicing integration involves several steps:

1. Inbound Processing (Receipt)

Incoming e-invoices in XML format (UBL, CII) or as ZUGFeRD PDFs must be automatically read and converted into the accounting software's internal data format. This includes:

• Detecting the invoice format
• Extracting all relevant data fields
• Validating the invoice against EN 16931
• Assigning the invoice to creditor accounts and cost centers

2. Outbound Processing (Dispatch)

When creating and sending e-invoices, the data from the accounting system must be converted into a compliant format:

• Exporting invoice data from the internal system
• Converting to XRechnung (UBL/CII) or ZUGFeRD
• Validating before dispatch
• Archiving the structured document

3. Archiving

E-invoices are subject to GoBD requirements and must be stored in an audit-proof manner for at least 10 years. The structured XML format must be retained in its original form — a PDF copy alone is not sufficient. For ZUGFeRD hybrid invoices, archiving the embedded XML portion is sufficient — the PDF representation only needs to be stored additionally if it contains tax-relevant information not present in the XML. A paper printout does not meet GoBD requirements.

The API-Based Approach

If your accounting software does not offer native e-invoicing support or if you use a custom ERP system, an API-based solution is often the most efficient path.

How It Works with invapi

invapi acts as middleware between your accounting software and the world of e-invoicing. The typical workflow looks like this:

Inbound:

1. An e-invoice arrives as XML or a ZUGFeRD PDF
2. The invapi API converts the invoice into a unified JSON format
3. Your system reads the JSON and creates the accounting entry

Outbound:

1. Your system exports the invoice data as JSON
2. The invapi API converts the JSON into XRechnung or ZUGFeRD
3. The validated e-invoice is sent to the recipient

Advantages of the API Approach

• Format-independent: invapi supports UBL, CII, and ZUGFeRD. Regardless of the format the recipient requires, you always use the same interface.
• Validation included: Every invoice is automatically checked against EN 16931 rules before it is sent.
• Future-proof: When standards or rules change, invapi updates the API. Your integration stays intact.
• Scalable: From 10 invoices per month on the free plan to unlimited volumes at the enterprise level.

Practical Example: Integration into a Custom ERP

A mid-sized trading company uses a custom-built ERP system based on PHP and MySQL. The integration with invapi was implemented in three steps:

1. Inbound module: Incoming XML invoices are sent to the invapi API via a cron job and returned as JSON. The ERP system reads the structured data and automatically creates journal entries.
2. Outbound module: When an invoice is created, the ERP exports the data as JSON, and the API returns a validated XRechnung.
3. Monitoring: API responses are logged to track which invoices were successfully validated and where errors occurred.

The entire integration was live within one week — without any changes to the existing ERP data model.

Conclusion

Integrating e-invoices into your accounting is the step that turns a legal obligation into a real productivity gain. Whether you use DATEV, lexoffice, sevDesk, or a custom system: an API-based middleware like invapi bridges the gap between your system and the required e-invoicing formats. Learn more on the integration page and get started with the free plan.