Invoicing API. FIZ issues the invoices and reports them to AT.
Your system sends the sale details and gets back the finished invoice, with its number and PDF. Claude and ChatGPT connect to FIZ without code and prepare invoices when you ask.
For the self-employed and companies, in every paid FIZ plan. A developer connects the API to your system once.
- Customer
- Ana Costa
- Total
- 61.50 €
- Draft created
POST /invoices - Number and ATCUD assigned
POST /invoices/{id}/issue - PDF ready
GET /invoices/{id}/pdf
Issued and reported to AT
How FIZ issues the invoices from your system
If you sell through an online shop, a CRM or your own app, the API removes manual invoicing: FIZ issues an invoice for every sale and reports it to AT.
FIZ receives the sale details
Your online shop, CRM or other system gives the customer, the items and the document type. FIZ saves a draft; only the issued invoice reaches AT.
FIZ issues the invoice and reports it to AT
When your system asks, FIZ numbers the invoice in its series, adds the ATCUD and the QR code and reports the invoice to AT. The response carries the number and the AT status.
FIZ prepares the PDF
On A4 with the template you choose in FIZ, or on 80 or 58 mm receipt paper. Your system gets the PDF and sends it to the customer.
What your system can ask FIZ to do
Your system uses an API key, which the owner, an admin or an editor creates on the Integrations page in FIZ. Each key works for one profile (self-employed or company).
- Invoices, receipts and credit notes
- Invoice, fatura‑recibo, simplified invoice and receipt, with discounts and withholding tax. Partial payments, each with its own receipt, and credit notes for the full amount.
- Customers and items
- Each item carries the IVA rate of the mainland, Madeira or the Azores, or the exemption reason. FIZ checks that every Portuguese NIF is typed correctly.
- Scheduled invoices
- FIZ issues them at the frequency you set, for example every month, reports them to AT and can email them to the customer.
- Repeated requests without duplicates
- If your system repeats a request with the same
Idempotency-Key, as in the example, FIZ returns the first response and creates no second document.
POST /invoicesx-api-key: fiz_api_••••••••Idempotency-Key: order-1042{ "type": "INVOICE_RECEIPT", "cae": "47711", "customerId": "66f2c1a9e4b0a1d2c3e4f5a6", "items": [ { "id": "66f2c1b7d3a1b2c3d4e5f6a7", "quantity": 2 } ], "payment": { "method": "mbWay", "date": "2026-10-09T10:15:00Z" }}Claude and ChatGPT prepare your invoices
With the FIZ connector, the assistant finds invoices, customers and items and prepares drafts when you ask. Before issuing, it shows the preview and waits for your confirmation.
You connect it without code, with a custom connector in Claude or ChatGPT. In FIZ, you choose the profile and the permissions you give the assistant, and you can disconnect it whenever you like.
What can the assistant do?
Look up customers, items, documents with their AT status, the transactions of the banks connected to FIZ and the expenses from e‑Fatura. Create customers, items, drafts and pro formas.
Issue invoices, record payments with a receipt, cancel documents and issue credit notes for the full amount, always after your confirmation.
- Request to the assistant
- Invoice Norte Studio for 2 hours of consulting.
- Customer
- Norte Studio, Lda
- Consulting · 2 h
- 120.00 €
- IVA 23%
- 27.60 €
- Total
- 147.60 €
- Your reply
- I confirm. Please issue it.
Issued and reported to AT
Partner apps: invoices in each customer’s name
Your app connects to FIZ through the API. Each customer has a profile, self-employed or company, and its owner authorises the connection. When the app asks, FIZ issues the invoices in the customer’s name.
Each customer pays for their own FIZ plan, or your platform pays for the customers’ access, by agreement with FIZ.
- In your app
- Name and domainInterfaceBilling for your product
- Outside your app
- Customer’s accountAT connectionManaging the connection
To test, the app connects without a paid plan to your profile and those of up to 20 people you list. Your customers connect to a production app approved by FIZ.
Choose a plan for your business
Frequently asked questions about the FIZ API
Which plans include the API?
Every paid FIZ plan, including during the free trial: Auto, Prime, Auto Pro and Prime Pro for the self-employed, and FIZ Pro and FIZ Max for companies. The connector for Claude and ChatGPT is in the same plans.
Do I need a developer?
Yes, to connect the API to your system or build an app: the developer works from the quick start guide and the API documentation. For Claude and ChatGPT, no: they connect without code, with a custom connector.
Are invoices issued through the API certified and reported to AT?
Yes, like the ones you issue in FIZ. FIZ is software certified by AT (No. 3041) and reports each document to AT when it is issued.
For this, the FIZ profile needs the AT connection, automatic invoice reporting switched on and an invoice series for this year. The API shows what is missing before issuing.
How does my system know that AT has received the invoice?
From the response to the issue request: it carries the number, the ATCUD and the status of the report to AT (in progress, reported or failed), with AT’s message. If it is still in progress, your system looks the document up again and gets the final status.
Which documents and data can I manage through the API?
With an API key: invoices, faturas‑recibo, simplified invoices, receipts, credit notes for the full amount, customers, items and PDFs, plus scheduled invoices, transport documents, pro formas and, read-only, the transactions of connected banks.
A partner app handles invoices, customers, items and PDFs. Declarations and expenses are handled in FIZ itself.
How can I test the integration?
With drafts: FIZ keeps them, your system can change them, delete them and generate the PDF, and only issued documents reach AT. Every document issued, even in a test, is a real fiscal document.
On a company profile, the invoices a partner test app asks for are issued only during the free trial or with a paid plan.
Can I invoice automatically when an order is paid?
Yes. When your online shop or system records the payment, it calls the API: it creates the draft of a fatura‑recibo and asks FIZ to issue it. FIZ reports it to AT and prepares the PDF, which your system sends to the customer.
Can my app invoice in the name of each of my customers?
Yes, with an app approved by FIZ. The owner of each profile authorises the connection and can disconnect it in FIZ at any time.
How does Claude or ChatGPT issue an invoice?
With your explicit confirmation, after showing you the preview in the conversation. If the document changes in the meantime, FIZ refuses to issue it until you confirm the new preview.
How do I connect Claude or ChatGPT to FIZ?
Add a custom connector in Claude or ChatGPT with the address https://api.fiz.co/mcp, and sign in to FIZ when the assistant asks. On the Integrations page in FIZ, under “Connect an assistant”, you will find the steps for each assistant.
Custom connectors depend on your Claude or ChatGPT plan.
How is my data protected?
An API key gives access to one profile only. An assistant or an app reaches only the authorised profile, with the permissions you gave it. On the Integrations page, you can revoke your keys and disconnect your assistants and the apps, with immediate effect.
In Claude or ChatGPT, the data the assistant receives from FIZ follows that assistant’s privacy rules.
Where is the API documentation?
At api.fiz.co, in Portuguese and English: the quick start guide, the API reference, the integration guide and the guide to connecting Claude and ChatGPT.
GitHub also has a sample app in Node.js and FIZ instructions for coding assistants, both open source.
Can my accountant see what the API issues?
Yes. Documents issued through the API stay in the same FIZ profile, with the others, and go into the invoicing SAF‑T (PT), which FIZ emails to the accountant every month if the owner turns this on. If the accountant has access to the profile, they also see them in FIZ.