SLF Data API

In preparation: not live yet

This page describes an interface we are preparing. It is not available yet, and details may change before launch. When it opens, access will be by invitation; you can register your interest below.

Read the full API documentation (draft)

If your company already issues invoices and records payments in its own system, such as an ERP, an online store or invoicing software, the SLF Data API is intended to let that system, once your developers have connected it, send those records directly to SLF Accounting for the books we keep for you. Those records would then no longer need to be exported to spreadsheets or sent as scans each month.

What you will be able to send and receive

  • Customer and supplier details, with their tax ID and branch number where they have one
  • Sales documents you issue, such as invoices, receipts, tax invoices, and credit and debit notes
  • Purchase documents you receive from suppliers
  • Records of payments received and made, including withholding tax certificates
  • Attachments such as PDF scans, linked to the records they belong to
  • A monthly summary from SLF of what has been recorded, so you can check it against your own system

How it will work

  • SLF will issue each company its own access key, with separate keys for testing and for live data. Keys will be replaceable, and SLF will be able to withdraw a key if needed.
  • Your system will send records one at a time over HTTPS, as JSON.
  • Each record will be accepted, or returned with the reason it could not be accepted, so you can correct it and send it again.
  • The API is being designed so that resending records you have already sent will not create duplicates.
  • Before going live, you will test against a separate test environment, so nothing reaches your real books until both sides are ready.
  • To protect returns SLF has already filed, once SLF has filed the return for a period, our system will lock the records in that period that would change it. If something locked needs correcting, your SLF accountant will handle it with you.

Before you start, we will ask for

  • A technical contact at your company
  • The system or systems the records will come from
  • Roughly how many documents you issue and receive each month
  • The document types you use

Technical reference

The draft integration guide and technical reference are published: a step-by-step quickstart, every endpoint and field, error codes, and an OpenAPI 3.1 file you can use to generate client code. They are in English and describe the interface as currently planned, so details may change before launch. Read the draft integration guide and reference · OpenAPI 3.1 (JSON)

Register your interest

Tell us about your company and the system you would connect. Registering does not give access yet; we will reply by email. Register interest

This page describes software that is still being planned. The features above may change or may not be offered, and nothing here is a commitment to provide the service or to a launch date. It is not tax or legal advice: which documents your company issues and how each transaction is taxed should be confirmed with your accountant.