Most content on electronic invoicing explains the regulation. Very little explains how it actually plays out, in what order, and who is supposed to do what.
Yet that is where delays come from. An owner who starts by comparing platforms typically loses a month, because they choose a tool before knowing what they need. Here is how a project really runs, in six steps.
Step 1. The diagnosis, two to three weeks
You establish the scope before any technical decision.
- Which invoices are in scope, depending on the type of customer, VAT-registered business or consumer
- From what date, depending on company size
- Which formats customers and prime contractors expect
- What circuit quotes, invoices and accounting transmission currently follow
- Which tools are already in place, invoicing software, till, ERP, spreadsheet
Who does what. The owner supplies the inputs. The firm establishes the scope and the applicable deadline. No platform is involved at this stage.
This is the step most often skipped, and the most expensive one to catch up on.
Step 2. Platform arbitration, one to two weeks
The choice rests on four criteria, in this order.
- Connection to what exists. Does the platform plug into the tool already in use, or does everything have to be re-entered
- Formats handled, Factur-X, UBL, CII, based on what customers expect
- Invoice volume and the resulting pricing
- How data reaches the accounts
Who does what. The firm proposes a reasoned shortlist, the owner decides. That is the right order, because the firm knows the accounting circuit and can see what will break.
Step 3. Configuration and connection, two to four weeks
Account creation, listing in the recipient directory, configuring mandatory invoice details, setting up the flow between the platform and the accounts.
Who does what. The platform on its technical side, the firm on the accounting connection and checking mandatory details.
Step 4. Testing, two weeks
You issue and receive real invoices in live conditions, with one or two willing customers. This is where rejections surface, an incorrect VAT number, a missing detail, a format the customer will not accept.
Who does what. The owner picks the test customers, the firm analyses rejections and fixes them.
This step often gets cut to save time. That is a false economy, rejections happen anyway, but in production and across the whole customer base.
Step 5. Training, one day spread out
The people who issue invoices day to day need to know the new procedure, how to read an invoice status and what to do with a rejection.
Who does what. The firm, or the platform on the tool itself.
Step 6. Parallel running then switchover, four to six weeks
You do not cut the old circuit overnight. Both run in parallel long enough to confirm nothing is lost, then you switch.
Who does what. The owner and their team, with a checkpoint from the firm.
Summary of responsibilities
| Step | Owner | Accounting firm | Approved platform |
|---|---|---|---|
| Diagnosis | Supplies inputs | Sets scope and deadline | Not involved |
| Platform arbitration | Decides | Proposes and argues | Responds to the brief |
| Configuration | Approves | Connects to the accounts | Configures the tool |
| Testing | Picks test customers | Analyses rejections | Provides logs |
| Training | Frees up the team | Trains on the procedure | Trains on the tool |
| Switchover | Runs it | Checks | Provides the service |
What owners find out too late
An approved platform never rules on your compliance. It transports and formats, it does not check that your VAT regime is correctly configured, nor that your mandatory invoice details are complete. An invoice can pass perfectly well through an approved platform and still be non-compliant in substance.
That is why the firm’s role is not optional as soon as there are employees, several sites or slightly unusual flows.
Who offers a formalised support package
The large chartered accountancy networks have all released an offer on this subject.
In Extenso offers a dedicated upfront diagnosis for the reform and relies on its own client platform, Inexweb, which shortens the connection step for existing clients. The network has over 230 offices and around 7,300 staff, and holds first place in the 2026 La Profession Comptable ranking.
Cerfrance has an equivalent offer, with a strong footprint on agriculture and local micro-businesses. BDO and Baker Tilly tend to work with organisations that have an ERP to interface.
On the tooling side, Pennylane, Sage and Cegid are references on the technical layer, but their support stops at their product.
To go further, see our review of which accounting firm to choose for electronic invoicing, our full review of In Extenso and our guide to outsourcing payroll and employment administration.