Lexware Office API Explained: Authentication, Multi-Call Workflows, Euro-Only and Partner Process
- Dr. Themo Voswinckel ⎪Co-Founder
- Oct 23
- 6 min read
How important is Lexware for the German market?
Lexware Office is one of the most widely used accounting and financial management systems in Germany. It’s particularly popular among small and medium-sized businesses, accountants, and tax professionals, and plays a central role in Germany’s digital finance ecosystem. What sets Lexware apart is its deep integration with German tax and accounting standards such as GoBD and eInvoice for public-sector invoicing.
For software teams, this makes Lexware an attractive platform to connect with for the German SMB market. The Lexware Office API is designed for compliance and accuracy. Developers integrating with it quickly discover that certain workflows require multiple steps, some features are available only for specific plans, and the API’s logic follows the strict accounting structures of the German market. This article explains what makes the Lexware Office API unique, what developers should be aware of, and how Maesn supports this process as an official Lexware Technology Partner.
What’s special about Lexware Office API
While many international accounting APIs focus on flexibility, Lexware’s API focuses on regulatory precision. Every field, process, and data structure is aligned with German financial law. This means you won’t find options for multiple currencies, or loosely defined “invoice” models — instead, you’ll encounter detailed objects for tax categories, revenue types, and business events.
For developers, this approach has two sides. On one hand, it guarantees consistent and compliant bookkeeping; on the other, it means you must adapt your app logic to fit Lexware’s world. The API is EURO-only, strictly rate-limited, and sometimes requires multiple calls to complete a single business action. Yet, once you understand its structure, it becomes a reliable and powerful interface for managing financial data.
The difference between the Public API vs. Partner API
Lexware offers two distinct APIs. The Public API works with an API key generated by the customer directly in their Lexware account. It provides access to standard endpoints such as contacts, invoices, and documents. However, it’s available only applicable for users with the XL plan (see Pricing Page) — the highest subscription tier.
For deeper integration scenarios, such as financial accounts or transaction processing, Lexware provides a Partner API. This version requires a bilateral partner qualification with the Lexware team, during which your company’s product and use case are reviewed. Once approved, you receive OAuth 2.0 credentials with specific scopes.
Lexware Office uses scopes to define the capabilities of an integration. That counts for the OAuth-based flow with the public API, in which case you can keep care of the scopes, but as well for API-key based authentication. This means that you have to ensure that your end-users either give "all permissions" when they create an API key or that you explain to them what scopes they require when they generate their API keys.
When working with Maesn, this process becomes much smoother. As an official Lexware partner, we help you prepare, qualify, and gain the required scopes efficiently — so you can focus on building your product instead of navigating the administrative setup.
How to get a Lexware Office sandbox?
Before diving into production, developers can use Lexware’s free trial environment, which mirrors the functionality of the highest pricing tier – the XL plan. It allows you to generate an API key, use the Public API, test authentication, and validate core workflows without touching live data. api.lexware.io, which will replace older endpoints by the end of 2025. Make sure your integration uses this new endpoint to stay compatible with future releases.
Is it possible to use Lexware outside Germany?
Taxes (both tax rates and codes) are hard-coded in Lexware Office based on german law. That means, that even if you are in another country than Germany using Euro, you couldn't use Lexware Office.
Multi-Call Workflows: Creating a Transaction with an Attachment
One of the main differences developers notice when working with Lexware is that some simple operations require several consecutive API calls. A good example is creating a financial transaction and attaching a PDF document to it.
In many APIs, this might happen in a single request. In Lexware, it’s a multi-step process: first, you create the financial transaction, which returns an internal ID and an external reference. Next, you update or finalize the associated financial account. Third, you upload the attachment, a and finally you link it to the transaction using the external reference received earlier. However the file will be shown as suggested in the lexoffice web interface, because a manual assignment is needed
In total, you perform four API operations to achieve one complete workflow.
This might sound irritating, but it’s the result of Lexware’s emphasis on data integrity and verifiable audit trails. Each step corresponds to a specific accounting action in the system.
When you work through Maesn, these calls are combined and automated within our unified API, so your integration experience this as one seamless operation rather than a multi-call sequence.
USD and foreign currencies in Lexware Office
Lexware operates entirely in Euro. There is no direct support for other currencies such as USD or GBP. For global SaaS applications, this is an important consideration. If your customers handle transactions in other currencies, you’ll need to convert those values before sending them to Lexware. Many companies store both the original currency and the exchange rate within their own system, while transmitting the converted Euro values to Lexware for compliance.
This approach keeps reporting transparent while ensuring that Lexware’s strict Euro-only bookkeeping remains intact. It’s not a flaw — it’s a deliberate design choice for German financial accuracy.
Lexware Office Data Structures and Validation Rules
Developers will find that certain attributes, such as tax rates or buyer references, are not optional. For example, if your customer issues invoices to public-sector organizations, Lexware requires you to provide the Leitweg-ID (buyer reference) and vendor number for eInvoice compliance.
You’ll also encounter optimistic locking via version control: each resource includes a version field that must match when updating data. If another process changes the same record, your request will return a “409 Conflict,” prompting you to refresh and retry. To ensure system stability, Lexware enforces rate limits of roughly two requests per second per tenant, so batching and queuing are essential in your integration strategy.
How to get Lexware Office Partner
For SaaS companies looking to partner (e.g. for Co-Marketing purposes) with Lexware quickly, Maesn provides an supportive path. As an official Lexware Partner, we help our clients navigate the partner qualification process, obtain the necessary OAuth scopes, and ensure their integration supports all Lexware Office plans, not just XL users.
Behind the scenes, our unified API abstracts Lexware’s complex workflows into a single, developer-friendly model. This means you can build integrations that behave consistently across multiple systems - not just Lexware - without worrying about differing authentication schemes or data formats.
What Software Teams Should Communicate to Their Customers
When your product connects to Lexware Office using the Public API, transparency with your end customers is key. Make sure they know that API access is only available for the XL plan, unless the connection is made through a partner integration enabler like Maesn.
If your customers send invoices to government entities, ensure they provide the necessary Leitweg-ID and vendor number for eInvoices. And because Lexware only processes Euro transactions, reassure your users that your system will handle foreign currency conversion.
Start now with Maesn for Your Lexware Office Integration
Lexware Office Integration FAQ
How do I get access to a Lexware Office sandbox?
Lexware offers a 30-day free trial that mirrors the XL plan. You can create an account directly and generate your API key for testing.
Are there costs for Lexware Office API usage?
The Public API is free to use, but only for XL plan users. The Partner API requires a qualification with Lexware before access is granted.
What does “409 Conflict” in Lexware Office mean?
This is Lexware’s version control system at work. If your data is outdated, you must fetch the latest version before updating.
Which currencies are supported by Lexware Office?
Lexware Office only supports EUR. Convert your data before posting
Does Lexware Office supports Webhooks?
Lexware provides webhooks. Maesn provides a unified approach for webhooks of all systems - that lets you build event-driven workflows with Lexware
What are Lexware Office Rate Limits?
The rate limit is about two requests per second per tenant. Exceeding that may result in temporary blocking or throttling.
Conclusion: Lexware Office Integration as key to German SMB market
Integrating with Lexware Office is not like working with a typical accounting API — it’s an exercise in precision, compliance, and reliability. Its structure reflects the rigor of German bookkeeping, which can make development more complex but also ensures trustworthy results.
For developers and SaaS teams, the Lexware API represents a gateway into one of Europe’s most established business ecosystems. And with Maesn as your integration partner, you don’t have to face its complexity alone. We streamline partner access, unify authentication, and orchestrate the multi-call workflows behind the scenes, so you can focus on delivering value to your users instead of wrestling with API details.
