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Pennylane provides an API to create or import customer invoices, send supplier invoices, manage customers and products and read ledger entries, using company or firm tokens. A business app connected to Pennylane usually costs $6,800 to $22,400 (€6,000–€20,000)excl. VAT.
Your business app produces quotes, service calls, sales or expense claims. Your accountants re-type them or receive them as PDFs. Connecting the two removes a task with no value and cuts errors. Pennylane comes up often because its API is public and documented: here is what it actually allows, based on its documentation as checked in October 2026, and how to proceed with other accounting software.
What the Pennylane API allows
The Pennylane API documentation describes several invoicing use cases: creating customer invoices in Pennylane, importing invoices produced by another system (ERP, CRM, billing tool), importing supplier invoices with their file, and linking invoice lines to products.
Access is controlled by scopes, either read-only or read-write.
| Area | Examples of documented scopes | Typical use for an app |
|---|---|---|
| Sales | customers, products, customer invoices, quotes, subscriptions | Create the customer and invoice from the app |
| Purchases | suppliers, supplier invoices | Send documents captured in the field |
| Accounting | ledger entries, journals, accounts, trial balance, FEC export | Read data for a dashboard |
| Banking | transactions, bank accounts | Show payment status |
| Files | attachments | Attach the supporting document to an invoice |
Three authentication methods are available: a company token, generated in Pennylane’s settings; a firm token, for access to several companies; and OAuth 2.0 for partner apps. The documentation also includes guides on tracking data changes and on webhooks, which help avoid polling the API constantly.
I did not find any plan requirement for API access on those pages: check your Pennylane subscription before starting.
Other accounting software
The reasoning is the same with other software; only the means change:
- Documented API: direct connection, in real time or in batches.
- Library or service to install: common for software installed on a company server.
- Import files: the app generates entries in the format the software expects. Less elegant, very reliable.
Whatever the method, I recommend starting with a single flow, often customer invoices, and running it for a month alongside the old process. Your accountant compares the two, we fix any category or VAT discrepancies, then add the next flows. It is slower on paper, but far safer than switching everything at once.
For the most common cases, see connecting a business app to Sage and connecting an app to Cegid.
Budget and timeline
Amounts exclude VAT and cover a first version running in production. The connection matches the “connection to other tools” building block in my pricing ($2,300 (€2,000)excl. VAT); the “quotes, invoices and PDF” block ($1,700 (€1,500)excl. VAT) is added if the app produces the invoices itself.
| Project | What it includes | Indicative budget | Timeline |
|---|---|---|---|
| Business app sending sales | Focused app + creating customers and invoices in Pennylane | $6,800 to $13,500 (€6,000–€12,000)excl. VAT | 1 to 2 months |
| App with quotes, invoices and sync | Quotes, invoices, PDFs, sending and payment status coming back | $11,200 to $22,400 (€10,000–€20,000)excl. VAT | 2 to 3 months |
| Full management tool linked to accounting | Several roles, purchases and sales, financial dashboard | $16,800 to $56,000 (€15,000–€50,000)excl. VAT | 3 to 6 months |
The estimator gives you a range in one minute based on the features you select.
Decisions to make before development
- Who numbers the invoices? One source, no exceptions. Two parallel numbering sequences create gaps and duplicates, which accounting will not accept.
- Who issues the e-invoice? Since the French reform, invoices between companies go through an accredited platform. Your setup has to be consistent with that choice: see mandatory e-invoicing in France.
- Which chart of accounts and categories? The app must send data your accountant can use without reworking it. I bring them into scoping.
- What happens with errors? A customer without a company ID, an unexpected VAT rate: each rejection must be visible and fixable by a user.
When this is not the right approach
If you issue your invoices directly in Pennylane and the volume stays reasonable, keep that tool: it already connects to accounting. Building an invoicing module only to reconnect it afterward makes no sense.
Custom software makes sense when the invoice comes from a process Pennylane knows nothing about: a service call approved in the field, an order placed in a customer portal, a completed route. That is the case with OptiRoad, a platform for mobile professionals that builds invoicing into route planning. To compare with off-the-shelf invoicing software, see the page on quote and invoicing software.
Where to start
- Map the journey of an invoice, from the event that triggers it to its payment.
- Bring your accountant in from the start: they know what is missing today.
- A 30-minute call to check feasibility with your accounting software.
- Scoping (1 to 2 weeks): flows, numbering, e-invoicing circuit, fixed quote.
- Development in batches, tested in a test environment before going live.
Frequently asked questions
Should invoices be created in the app or in Pennylane?
Both are possible. The API can create an invoice in Pennylane from products and templates, or import an invoice already produced by another system. The right choice depends on which tool owns invoice numbering and how you issue your e-invoices.
Can my accounting firm access the data?
Pennylane provides company API tokens and firm tokens, the latter giving access to several client companies. Your app should connect with a company token limited to the scopes it needs.
What if I use different accounting software?
The principle is the same: an API if the vendor offers one, otherwise file exports in the software’s import format. The pages on Sage and Cegid go into their options.
Does France’s e-invoicing reform change anything?
Yes. Invoices between French companies must go through an accredited platform, following the official timeline. Your app has to fit into that circuit, either directly or through the tool that issues your invoices.