ChatGPT App — Create Invoices from ChatGPT

The invoice card and PDF downloads support German, English, French and Italian. The PDF uses the chat language or an explicitly requested document language; the download link preserves that choice even when opened in another browser. Your own text, such as line items and customer names, is not translated.

With the Slonge app for ChatGPT you create Swiss invoices in CHF with VAT (MwSt) and a QR-bill straight from a ChatGPT conversation. You describe the invoice in your own words, ChatGPT creates it in Slonge Billing as a draft and, if you ask, gives you the PDF link.

Requirements

• A Slonge account with a role that may manage invoices (Accountant or Administrator).
• An IBAN configured under Settings, so the invoice includes a QR-bill.
• A ChatGPT plan that supports apps or developer mode. See OpenAI's documentation for which plans qualify.

Connecting

1. In ChatGPT, open the app management and add the Slonge app (Connect).
2. Sign in to Slonge Billing if you are not signed in yet.
3. Review the consent screen: it shows which access the app will get.
4. Click Approve. ChatGPT is now connected to your Slonge account.

Example prompts

• "Create an invoice for Müller AG for 2 hours of web design at CHF 150, 8.1% VAT."
• "Find the customer Muster GmbH and create it if it does not exist yet."
• "Show me my open invoices."
• "Give me the PDF link for the latest invoice."
• "Send invoice RE-2026-0042 to the customer by email."

What the app can do

1. Find customers
2. Create customers
3. Create an invoice as a draft — never sent directly
4. List invoices
5. Create a PDF download link — the link is valid for 10 minutes
6. Send an invoice by email — only after you explicitly confirm

Downloaded invoice PDFs include the company logo stored in Slonge, without requiring a signed-in browser to load it.

What the app cannot do

• Delete anything.
• Change settings.
• Access accounting or bank data.
• Take or trigger payments.

VAT rate

The app asks which rate applies and never guesses: 8.1% (standard), 2.6% (reduced), 3.8% (accommodation) or 0%. It is best to state the rate in your prompt.

Security & privacy

• Sign-in uses OAuth with PKCE. ChatGPT never sees your Slonge password.
• Access is narrowly scoped (only the capabilities above).
• The access token is valid for 1 hour; it is renewed with a refresh token that rotates on every use.
• You can revoke the connection at any time under Settings → API, where it appears as "<app> (OAuth)".
• All actions of the app are recorded in the audit trail.
• Important: because you ask ChatGPT to create the invoice, invoice content (for example customer names, line items and amounts) passes through OpenAI/ChatGPT. Do not enter data in these chats that you would not want OpenAI to process.

Troubleshooting

See also: API & MCP for API tokens and other AI clients.