POST /v1/einvoice/create · 1 cent per operation

Create an e-invoice (XRechnung or ZUGFeRD)

Turn simple invoice data (JSON) into an XRechnung (UBL or CII) or a ZUGFeRD PDF/A-3 with embedded XML. We calculate the totals and VAT; every invoice must pass the official KoSIT check before you get it.

Try it

curl -X POST https://api.bigapi.dev/v1/einvoice/create -H 'Authorization: Bearer $KEY' -H 'Content-Type: application/json' -d '{"format":"zugferd","number":"RE-2026-0042","issue_date":"2026-10-17","seller":{"name":"Muster GmbH","street":"Hafenstrasse 5","zip":"20459","city":"Hamburg","vat_id":"DE136695976","email":"rechnung@muster.example","phone":"+49 40 1234567"},"buyer":{"name":"Kunde AG","street":"Ring 1","zip":"10115","city":"Berlin","email":"eingang@kunde.example"},"payment":{"iban":"DE89370400440532013000"},"lines":[{"name":"Beratung","quantity":2,"unit":"hour","price":95}]}' -o rechnung.pdf

New keys come with 100 free operations, no signup: curl -X POST https://api.bigapi.dev/v1/keys. Failed calls cost nothing.

Parameters

Name	Meaning
`number` required	Invoice number.
`issue_date` required	Invoice date as YYYY-MM-DD.
`seller` required	Seller: name, street, zip, city, country (default DE), vat_id or tax_number, email, phone, contact. XRechnung needs email and phone.
`buyer` required	Buyer: name, street, zip, city, country, email (electronic address for XRechnung), vat_id for reverse charge.
`lines` required	Items: name, quantity (default 1, up to 4 decimals), unit (piece, hour, day, kg, lump sum … or a UN/ECE code), price (net, up to 4 decimals), vat_rate (default 19 for German sellers, otherwise required), vat_category (S, Z, E, AE, K, G, O; default S). Discounts as an extra line with negative quantity.
`format`	ubl or cii give an XRechnung 3.0 XML; zugferd gives a PDF/A-3 with factur-x.xml (profile EN 16931). Allowed: `ubl`, `cii`, `zugferd` Default: ubl
`buyer_reference`	Leitweg-ID for public buyers, otherwise e.g. order or customer number. Required for XRechnung (falls back to order_reference). Default: none
`due_date`	Payment due date, YYYY-MM-DD. Default: none (then 'payable immediately' for XRechnung)
`delivery_date`	Delivery or service date, YYYY-MM-DD. Default: none
`payment`	iban, bic, account_name, reference. XRechnung needs an IBAN for bank transfer. Default: none
`small_business`	true for German small businesses (§ 19 UStG): all items without VAT, with the legal note. Default: false
`type`	credit_note gives a credit note (UBL CreditNote, type 381); add preceding_invoice {number, date}. Allowed: `invoice`, `credit_note` Default: invoice
`lang`	Language of the readable PDF (zugferd only). Allowed: `de`, `en` Default: "de"
`order_reference`	Purchase order number. Default: none
`prepaid`	Amount already paid; reduces the amount due. Default: 0
`note`	Free text note on the invoice. Default: none

Result and price

1¢ · 1 cent per operation

Returns application/xml | application/pdf. Response headers carry the cost (X-BigAPI-Cost) and notes about your input (X-BigAPI-Warnings).

Good to know

Totals and VAT are calculated by us in exact decimals: line = quantity × price, VAT per rate on the sum of its lines, rounded commercially to the cent (half away from zero).
Every invoice is checked with the KoSIT validator (XRechnung configuration 3.0.2) before it leaves the server. The response header X-BigAPI-Einvoice-Checked says so.
German small businesses: set small_business to true. All items get category E with the note "Gemäß § 19 UStG wird keine Umsatzsteuer berechnet."
ZUGFeRD output is a PDF/A-3b with factur-x.xml (profile EN 16931) and a readable invoice page. It is a format accepted for e-invoices in Germany; whether the content is right for your tax case is not something any tool can check.

Errors your agent should handle

`400 invalid_invoice_data`	A field is missing or wrong; the response names it in "field" and says what is needed (e.g. buyer_reference for XRechnung).
`422 invoice_invalid`	The invoice was built but does not pass the official KoSIT check; you get the rule codes instead of a file. Nothing is charged.

From an agent (MCP)

Connect BiGapi as an MCP server: https://api.bigapi.dev/mcp (hosted) or npx -y @bigapi/mcp (local). Then ask in plain words; the agent finds einvoice_create on its own.

Create an XRechnung for invoice RE-2026-0042 to the city of Musterhausen, Leitweg-ID 04011000-1234512345-06, two hours of consulting at 95 euros.

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