Pennylane API Integration Explained: Sandbox Setup, OAuth Credentials, and Rate Limits for Developers

Lennart Svensson
Oct 20
5 min read

Pennylane has quickly become one of the most recognized accounting platforms in France and is now expanding into other European markets. The platform combines bookkeeping, financial management, and collaboration between businesses and accountants. —It's growing relevance making it an attractive choice for software vendors that want to connect their product with their solution.

However, building a reliable Pennylane API integration requires understanding its structure, rules, and API specifics.This article walks you through the key points developers should know — from sandbox access to rate limits — and shows how Maesn helps software teams build scalable, multi-system integrations that just work.

Visual showing DATEV and SaaS intgration — Integrating Pennylane API via Maesn Unified APi

Getting a Pennylane Sandbox

Before you can start developing against the Pennylane API, you’ll need access to their sandbox environment. Unlike many APIs where developers can instantly create test credentials, Pennylane’s sandbox requires a manual onboarding process. You’ll need to contact the partnership team, share company details, and specify your intended scopes and data access. This approach ensures data protection and quality — but it can also extend your initial development timeline.

👉 With Maesn, developers get instant access to a Pennylane self-service sandbox that mirrors Pennylane’s behavior, with persistent credentials and consistent test data structures. That means you can prototype integrations, without waiting for manual approval.

How to Create a Pennylane Application

Once sandbox access is approved, the next step is to create an application to receive client credentials. This process includes defining the Pennylane scopes (permissions) your app needs - for example, access to invoices, customers, suppliers, transactions, or journal entries.

Each scope must be reviewed by Pennylane’s team, which ensures data is accessed responsibly. However, this can require some back-and-forth communication before credentials are activated — especially if your integration spans multiple accounting workflows (like both Accounts Payable and Accounts Receivable).

👉 With Maesn, scope management is streamlined. We support you in your scope specification process. Whether it’s retrieving AP invoices, posting AR data, or reading journal entries, you develop once and it works across all supported accounting systems.

Understanding Pennylane API Credentials

When your Pennylane application is created, you’ll receive a client ID and secret. These credentials are used to authenticate your app via OAuth. One key detail: the credentials are only valid for 7 days unless refreshed. This short lifespan adds an extra layer of security but can complicate development if your team frequently deploys, tests, or automates integrations.

👉 Maesn’s Unified API enables persistent credentials that remain valid across environments. We manage token rotation and expiration automatically - so your engineering team can focus on data flows, not credential maintenance.

Handling Pennylane Data Models

Pennylane’s API follows a structured accounting logic, but some data relationships require multiple endpoints. For example, creating a customer might involve:

Creating a “person” record,
Linking that person to a company,
Adding a contact role.

This ensures accounting data integrity, but for developers, it means more calls, dependencies, and error handling.

This becomes particularly relevant in workflows like:

Accounts Payable: managing supplier details and purchase invoices
Accounts Receivable: creating customer invoices and tracking payments
Transactions and Journal Entries: posting financial records to the ledger

👉 Maesn simplifies this complexity through our unified data schema. Your integration interacts with standardized “customer,” “supplier,” “invoice,” or “transaction” objects and Maesn handles the Pennylane-specific orchestration behind the scenes.

Connecting Customers and Suppliers in Pennylane

In Pennylane, customer and supplier data are separate but closely related objects, each with their own endpoints. When you need to create or update both sides (for example, when your product manages invoices or vendor bills), you’ll need to handle both relationships properly to avoid missing data links.

👉 Maesn unifies customer and supplier handling across accounting systems. You use one consistent endpoint, and we map it to the appropriate structure in Pennylane, Sage, DATEV, or other systems — maintaining referential integrity between your CRM or ERP and the accounting layer.

Invoices, Documents, and Attachments

Invoices and documents are central to Pennylane’s API, but managing them requires attention to detail:

Files (PDFs, receipts) must be encoded and uploaded via specific endpoints.
Metadata (dates, due amounts, supplier/customer references) must align with journal entries.
Some endpoints distinguish between sales invoices (AR) and purchase invoices (AP).

This setup gives accountants precise control but adds complexity for developers who want to sync documents automatically.

👉 Maesn standardizes invoice and document handling. You post invoices once — with attached documents and Maesn translates them into Pennylane’s correct structure. It’s designed for end-to-end automation of invoice lifecycle events: creation, approval, and reconciliation.

Journal Entries and Transactions

Journal entries are at the heart of any accounting integration, but they often vary widely between platforms.Pennylane exposes them through granular endpoints, meaning developers must carefully build transaction posting logic (including debit/credit lines, ledger accounts, and reconciliation markers).

👉 With Maesn, journal entries, transactions, and ledger operations follow a unified model.We normalize field names and validation rules, so your product can sync general ledger data seamlessly across Pennylane and other accounting systems — without custom rework for each provider.

Rate Limits in the Pennylane API

Pennylane enforces clear API rate limits to protect performance and stability:

4 requests per second for most endpoints
2 requests per second for customer invoices

For integrations processing high data volumes (for instance, nightly invoice syncs or historical imports), this requires careful queueing and throttling to avoid 429 Too Many Requests errors.

👉 Maesn’s API gateway manages rate-limit compliance automatically.We queue, retry, and batch requests intelligently — ensuring throughput without hitting Pennylane’s limits, and letting you handle bulk AP/AR synchronization efficiently.

User Roles and Plan Requirements

To activate integrations in Pennylane, the end user must:

Have an Essential plan or above, and
Hold the “gestionnaire” (manager) role in their company workspace.

Without these permissions, the user won’t be able to authorize the connection, which can cause confusion during onboarding.

👉 Maesn makes onboarding smoother by checking plan and role requirements automatically.If a user isn’t eligible, they receive a clear, guided prompt — reducing failed connections and support tickets.

Summary: Building a Reliable Pennylane Integration

Pennylane’s API is designed for compliance, precision, and collaboration — but that comes with some technical depth.From sandbox access and manual credential handling to multi-step data models and rate limits, it demands thoughtful engineering.

With Maesn’s Unified API, software teams can build once and scale across accounting systems like Pennylane, Sage, DATEV, and others.Our abstraction layer standardizes: