What to look for in an e-invoicing API?

For European software vendors, e-invoicing is a strategic decision that impacts your product roadmap, compliance responsibilities, and ability to scale. Whether you’re building ERP, accounting, or fintech software, e-invoicing should be a key part of your product.

We've explored the critical decision of build vs. buy and broke down the true cost of building e-invoicing in-house. While building in-house might seem manageable at first, the long-term costs, regulatory changes, operational overhead, and cross-border complexity, often outweigh the initial benefits. Embedding a partner API, such as Maventa's on the other hand, offers a way to simplify compliance requirements, reduce maintenance, and scale efficiently.

This guide continues the conversation by focusing on what makes a great embedded e-invoicing API. We’ll break down the key factors to consider when choosing a partner that becomes part of your infrastructure and your long-term success.

Multi-country coverage aligned with your growth strategy

The first consideration is geographical: which countries does the provider support?

The bare minimum of coverage is rarely enough, but it's about the depth of that support, the speed at which new mandates are integrated, and the provider’s understanding of local nuances. 

Example: A SaaS accounting platform expanding from Germany to Italy faced delays because their e-invoicing provider didn’t fully support Italy’s SDI requirements. The provider relied on third-party integrations, which introduced errors and slowed down customer onboarding. A partner with native support for Italy’s e-invoicing system could have avoided these issues entirely.

So if your roadmap includes multi-country expansion, you’ll want to know:

• How new markets are onboarded

• Whether coverage is native or bought through a partner and pieced together

• How regulatory updates are handled once you’re live

The e-invoicing API provider should make expansion as simple as possible. Maventa’s API, for instance, supports multiple EU markets and formats like Peppol and XRechnung. Its automatic format conversions and smart routing ensure invoices are delivered in the correct format, no matter the recipient’s preferences. This kind of built-in flexibility is critical for scaling across borders.

Compliance ownership should not be a shared burden

One of the main reasons to choose an embedded API partner is to outsource compliance and regulatory tracking to the vendor. This only works if the partner takes clear responsibility.

A strong e-invoicing provider actively monitors regulatory changes, updates formats and validation rules, and implements these changes without disrupting anything in your product. You shouldn’t have to reconfigure your product every time a mandate changes.

Ask directly: What happens when regulations evolve? What’s required on our end?
The best answer is: almost nothing.

This proactive approach is essential, especially with regulations like ViDA and Peppol mandates evolving rapidly. Providers like Maventa, with nearly 20 years of experience in e-invoicing, take full ownership of compliance, allowing software vendors to focus on their core business.

Developer-friendly integration that respects your time and roadmap

An embedded API integrates directly into your product. If it’s difficult to work with or even get started with, your team will feel the impact immediately.

Look for:

• Modern, stable API technology

• Realistic sandbox and test environments that you have an easy access to

• Predictable versioning and easy-to-follow change communication

• Documentation written by developers, for developers

For your developers, usability issues can mean the difference between a quick launch, or weeks, even months of frustration. 

Operational reliability you can trust to just work

E-invoicing is customer-facing infrastructure. When it fails, it fails visibly. Your partner API should handle the operational heavy lifting: routing, acknowledgements, retries, error handling, and monitoring across networks. Equally important, they should have robust incident management processes and transparency.

Clear uptime commitments and support models are confident indicators of how seriously the provider treats their infrastructure and how committed they are to serving you when problems arise. If they are not processing millions of transactions a month, is their solution going to be able scale along with you? 

Predictable commercial models and pricing

E-invoicing costs typically scale with volume and geography. That’s expected, but it should also be easy to predict when the pricing model is transparent.

E-invoicing pricing models should scale predictably, be easy to forecast, and easy to explain internally or passed on to customers if necessary. Be cautious of models that appear simple initially but become more complex as transaction amounts grow. Hidden fees for e.g. onboarding or format conversions can make for a real surprise when you have already committed. 

Readiness beyond invoices

Even though it can sound like a cliche, the future is going to be even more digital, and invoices are rarely the full story when it comes to electronic document handling. Depending on the market, related documents like credit notes, orders, delivery notes, or reporting obligations often follow. The Peppol network already offers automation and digitalisation possibilities for multiple different document types. 

Even if you don't need support for other document types right now, choosing an API with the capacity to grow your document scope minimises future rework and reintegration. 

Long-term partner, not just a vendor

Finally, remember this: an embedded e-invoicing API is a (at least semi-) permanent part of your product stack. Track record, experience with regulatory changes, and stability matter. You’re not buying a one-off functionality, but rather trusting your customers' business-critical transactions to this partner. That’s worth evaluating carefully. 

With Maventa’s expertise, you can enable e-invoicing to without the burden of managing it, allowing you to focus on what you do best.  Contact our team to explore how Maventa can become your trusted e-invoicing partner.