How to Write a Compliant
Invoice for AI Training Platforms

Our main Germany tax guide covers registration, the Kleinunternehmerregelung, and annual declaration. This article is narrower and more practical: the actual invoice document you may need to produce, with the exact required fields and legal language.

This article provides general informational context, not professional tax or legal advice. Invoicing requirements can vary by specific situation. Verify your exact requirements with a Steuerberater if your situation involves anything beyond straightforward freelance income.

Do You Actually Need to Send an Invoice?

This is worth clarifying first: most AI training platforms, including Mercor and SME Careers, handle payment directly through their own systems (Stripe, Deel, and similar) without requiring you to submit a separate invoice document. However, if you're working with a specific client, project, or platform that does request one — or if you simply want clean documentation for your own records — German invoicing law under § 14 UStG still applies to whatever invoice you produce.

Required Fields on a Compliant German Invoice

• Your full name and address
• The client's full name and address
• Your tax number (Steuernummer) or VAT ID (USt-IdNr.) if you have one
• A unique, sequential invoice number (e.g., RE-2026-001)
• The issue date
• A description of the service provided
• The quantity (often hours worked, for AI training task-based income)
• The rate and total amount
• Applicable VAT, or the Kleinunternehmer exemption sentence if applicable

The Mandatory Kleinunternehmer Sentence

If you're registered under the Kleinunternehmerregelung — covered in detail in our main tax guide — every invoice you issue must include this specific declaration:

"Gemäß § 19 UStG wird keine Umsatzsteuer berechnet."
(No VAT is charged according to § 19 of the German VAT Act.)

This sentence is not optional phrasing — it's the specific legal language required to declare your small business exemption status on the document itself. Omitting it, or charging VAT you're not registered to collect, creates a real compliance problem.

Invoice Numbering

Invoice numbers must be unique and sequential — you cannot reuse a number, even from a cancelled invoice. A common, clean format is year plus sequential number: RE-2026-001, RE-2026-002, and so on. Keep a simple running log so you never accidentally duplicate or skip a number.

Currency Considerations for AI Training Income

If you're invoicing a US-based platform or client directly (rather than receiving automated platform payments), specify the currency clearly. Since most platforms pay in USD, as we cover in our payment methods guide, your invoice should state the amount and currency explicitly, even though the actual payment and conversion happen separately through your chosen payment method.

The 2025/2026 E-Invoice Transition

As of January 1, 2025, German businesses must be able to receive electronic invoices (E-Rechnung) for domestic B2B transactions, with broader e-invoicing requirements phasing in over subsequent years. This is most directly relevant if you're invoicing German business clients specifically, rather than international AI training platforms — but it's worth knowing about as the broader compliance landscape shifts, particularly if your freelance work expands beyond AI training platforms into other German B2B clients.

How Long to Keep Your Invoices

Invoices must generally be retained for at least 8 to 10 years from the date of issue, depending on the specific record category under German tax law. Keep digital copies organized by year — this matters directly if your income crosses the Kleinunternehmer threshold and your records are reviewed.

A Simple Template Structure

The Bottom Line

Most of the time, AI training platforms handle payment without requiring you to issue a formal invoice. When you do need one — for a specific client, project, or your own clean records — make sure it includes all required fields, the exact Kleinunternehmer sentence if applicable, and a properly sequential invoice number. Keep digital copies for the full retention period required under German law.