PromptInvoice for agents

An AI agent can make an invoice, quote, estimate, receipt or payment voucher as a finished PDF with one HTTP request. The PDF is identical to the one the Download PDF button produces. No account, no key, nothing stored.

Quick start

curl -sS https://invoice.flowsxr.com/api/pdf \
  -H 'Content-Type: application/json' \
  -o invoice.pdf \
  -d '{
    "number": "INV-0042",
    "from": { "name": "Studio Nova Ltd", "email": "billing@studionova.com" },
    "to":   { "name": "Acme Corp", "email": "ap@acme.com" },
    "items": [ { "description": "Prototype development", "qty": 24, "rate": 120 } ],
    "currency": "NZD", "taxRate": 15, "taxLabel": "GST"
  }'

Python

import requests

doc = {"number": "INV-0042", "from": {"name": "Studio Nova Ltd"}, "to": {"name": "Acme Corp"},
       "items": [{"description": "Prototype development", "qty": 24, "rate": 120}], "currency": "NZD"}
r = requests.post("https://invoice.flowsxr.com/api/pdf", json=doc, timeout=60)
if r.status_code == 400:
    print(r.json()["details"])          # [{"field": "...", "message": "..."}]: fix and resend
r.raise_for_status()
open("INV-0042.pdf", "wb").write(r.content)

JavaScript

const r = await fetch('https://invoice.flowsxr.com/api/pdf', {
  method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify(doc),
});
if (!r.ok) throw new Error(JSON.stringify(await r.json()));
const pdf = new Uint8Array(await r.arrayBuffer());

Choosing the document type

Every field

Only number, from.name, to.name and at least one item are required. Everything else has a sensible default. Unknown fields are ignored and reported back as warnings.

Never send totals. Subtotal, discount, tax and total are always calculated from the items, exactly as the app does, so the PDF always adds up. A total field is ignored with a warning.

Examples

Payment voucher (paying a contractor)

{
  "docType": "voucher",
  "number": "PV-2026-014",
  "issueDate": "2026-10-02",
  "from": { "name": "Studio Nova Ltd", "email": "billing@studionova.com", "address": "12 Example Street\nAuckland 1010" },
  "to": { "name": "Jane Contractor", "email": "jane@example.com" },
  "items": [
    { "description": "Design services, September 2026", "qty": 1, "rate": 350 },
    { "description": "Advance for October 2026 (deducted from the October payment)", "qty": 1, "rate": 200 }
  ],
  "currency": "SGD",
  "paymentMethod": "Bank transfer",
  "approvedBy": "Alex Owner"
}

Invoice with tax, discount and bank details

{
  "number": "INV-0042",
  "issueDate": "2026-10-02",
  "dueDate": "2026-10-16",
  "from": { "name": "Studio Nova Ltd", "taxId": "123-456-789", "address": "12 Example Street\nAuckland 1010" },
  "to": { "name": "Acme Corp", "email": "ap@acme.com", "reference": "PO-2026-014" },
  "items": [
    { "description": "Mixed-reality prototype: Unity development", "qty": 24, "rate": 120 },
    { "description": "On-site user testing session", "qty": 2, "rate": 450 }
  ],
  "currency": "NZD", "taxRate": 15, "taxLabel": "GST",
  "discountType": "percent", "discountValue": 5,
  "customFields": [ { "label": "Project", "value": "September prototype" } ],
  "paymentDetails": "Bank: Example Bank\nAccount: 01-0000-0000000-00\nReference: INV-0042"
}

Logo and signature

Send images inline as base64 data URIs (PNG, JPEG, WebP or SVG, up to 1 MB each). Links to images are not fetched. The signature is printed above "Approved by" on vouchers and as the authorised signature on other documents.

import base64
logo = "data:image/png;base64," + base64.b64encode(open("logo.png", "rb").read()).decode()
doc["from"]["logo"] = logo

Responses and errors

{
  "error": "The document has problems. Fix the fields listed and send it again.",
  "details": [
    { "field": "number", "message": "is required" },
    { "field": "items[0].rate", "message": "must be a number (the unit price)" }
  ]
}

The first request after a quiet period can take a few seconds while the renderer starts. Later ones take about a second.

Rules for agents working for a person

1. Use only figures the person gave you or that come from their records. Never invent rates, hours, tax rates or bank details.
2. Pick the right type. Money coming in is an invoice (or a receipt once paid). Money going out is a voucher.
3. Show a summary before you generate: type, number, payee or client, each line, currency and the total you expect. Generate after they confirm.
4. Keep numbering consistent with the person's existing documents (ask for the last number if you do not know it).
5. Dates are YYYY-MM-DD. If the person says "today", use their local date, not yours.
6. Hand back the file, named as the Content-Disposition suggests, and say where you saved it. Sending it to anyone is the person's decision.
7. The API does not save anything. If the person wants the document in their PromptInvoice history, they can recreate it in the generator at invoice.flowsxr.com and press Save.

Limits and privacy

• Body up to 4 MB, up to 200 line items, up to 10 custom fields, images up to 1 MB each.
• Nothing is stored. The document is rendered and discarded. Each request records one anonymous usage event (status, document type, currency, number of lines, caller type such as curl or Python, and approximate location from the IP: country, region, city) in Google Analytics. Never names, amounts or any document text.
• While rendering, the page cannot reach any other website, so content in your document cannot load remote resources.
• Free to use. Please keep automated volume reasonable.
• Machine-readable summary: GET /api/pdf. Short pointer for LLM crawlers: /llms.txt.
• Source and self-hosting: github.com/prasanthsasikumar/PromptInvoice (MIT).