Enterprise AI API Procurement and e-Invoicing in Türkiye: an End-to-End Guide for Purchasing and Accounting

To receive a compliant Turkish e-invoice for an enterprise AI API subscription, you need a supplier registered as a taxpayer in Türkiye. On Onysoft AI Gateway you enter your tax number (VKN) in the billing details and click "Query GİB": the system performs a live lookup against the tax authority registry — if your company is an e-Fatura taxpayer, your legal title auto-fills and an e-Fatura is issued; otherwise an e-Arşiv invoice is issued automatically. Everything is billed in Turkish lira at the central bank (TCMB) rate.

A quick clarification: most results for this query describe OCR tools that read invoices with AI. This article covers the opposite — the process of procuring the AI API itself as a company: how it gets invoiced, how the tax treatment works, how to budget it, and how to evaluate the vendor.

An engineering team can trial a model in minutes; what turns a trial into a corporate purchase happens at the purchasing and accounting desks. This guide walks through the real mechanics of the e-Fatura/e-Arşiv flow, the KDV-2 (reverse-charge VAT) and withholding difference between foreign and domestic purchases, and what the same workload costs per model in lira — using live catalog prices.

Why Is the Invoice the First Question Accounting Asks in an Enterprise AI Purchase?

Because an API subscription the engineering team starts in minutes can crawl for weeks at the expense-documentation stage: a foreign provider's USD card receipt is not a substitute for an e-invoice in Turkish accounting practice. In an enterprise purchase the decision is never one person's — engineering looks at model quality, purchasing at contract and vendor risk, accounting at documentation and tax; the process moves at the speed of the slowest link.

With a foreign purchase, the file that lands on accounting's desk typically looks like this: a USD charge on the company card, a card receipt or a foreign-format invoice attached, an exchange-rate gap between the day of spend and the statement date, and a monthly recurring question about how to book the expense. Add to that the reverse-charge tax obligations detailed below.

With a supplier registered in Türkiye, that file collapses into a single document: an e-Fatura or e-Arşiv invoice issued to tax-authority (GİB) standards, denominated in lira. The document is legally defined, shows VAT on its face, and imports directly into accounting software. That is why, in an enterprise evaluation, "who issues the invoice and how" rationally comes before "which model is better".

What Are the KDV-2 and Withholding Burdens on Foreign AI Subscriptions, and What Changes with a Domestic Invoice?

When paying for electronic services purchased from abroad, a Turkish company may face the obligation to self-assess VAT as the responsible party (in practice, the KDV-2 return) and to evaluate withholding tax depending on the payment type; with a lira invoice from a supplier registered in Türkiye, these obligations do not arise. The difference is less about the total amount paid than about the accounting operation itself.

The mechanics: the party buying the service from abroad calculates the VAT the foreign seller cannot declare in Türkiye and declares it in its own name as the responsible party; whether withholding applies is assessed separately by payment type. In practice this means extra recurring return lines every month, currency-conversion bookings, and a "which category does this item fall under" debate — the operational load is fixed even when the amounts are small.

On a domestic invoice, VAT is shown on the invoice itself and is deductible under the general rules; the reverse-charge and withholding agenda simply never opens. Onysoft issues invoices in lira, and usage is deducted from your balance at the current TCMB rate — the currency conversion is done by the system, not by your bookkeeping. At month-end close, accounting holds a uniform, single-currency, standard expense document.

This section is not legal or tax advice; obligations vary with your company and contract structure — consult your own tax advisor.

Budgeting in Lira: What Does the Same Workload Cost per Month on Each Model?

Model choice creates a budget difference of more than 40x — which is why the budget line should not read "AI API" but "which task on which model". Concretely: suppose an internal app that summarizes customer correspondence makes 100,000 requests a month, each consuming on average 2,000 input and 300 output tokens. The monthly cost of that same workload at live catalog sale prices:

Model	Monthly cost (USD)	Monthly cost (TRY)	Class
deepseek/deepseek-v4-flash	$54.60	₺2,596.50	Economy
openai/gpt-5.6-luna	$57.00	₺2,710.64	Economy
anthropic/claude-haiku-4.5	$525.00	₺24,966.38	Speed
google/gemini-3.6-flash	$787.50	₺37,449.56	Speed
anthropic/claude-sonnet-5	$1,050.00	₺49,932.75	Flagship
anthropic/claude-opus-5	$2,625.00	₺124,831.88	Flagship

Measured: August 5, 2026 — api.onysoft.com live catalog. Scenario: 100,000 requests/month × (2,000 input + 300 output tokens). TRY equivalents calculated at the August 5, 2026 TCMB rate (1 USD = 47.555 TRY).

The takeaway to bring into the budget meeting: there is roughly a 46x gap between the two extremes, and most enterprise workloads (summarization, classification, data extraction) run comfortably in the economy/speed classes. Reserving flagships for the few critical tasks is the decision that actually sets the invoice. All 708+ models in the catalog draw from one balance; for the full pricing logic see the AI API pricing guide.

How It Works on Onysoft: Five Steps from Tax Number to e-Invoice

The flow from sign-up to the accounting file is five steps, and the invoice type is determined by the system, not by you:

1. Sign up: Open an account at api.onysoft.com/register; verify e-mail and phone.
2. Billing details: Enter your company's tax number (VKN) in the billing details section of the dashboard.
3. "Query GİB": The button performs a live lookup of your VKN in the tax authority registry. If your company is an e-Fatura taxpayer, your legal title auto-fills and your invoices are issued as e-Fatura; if not, as e-Arşiv. Manual title entry, wrong invoice types, and reject/refund loops disappear.
4. Lira balance: Top up by card or bank transfer; invoices are issued in TRY and usage is deducted at the current TCMB rate.
5. Documentation: Every API response returns the realized cost and the dashboard shows the lira equivalent; at period end, the usage report is downloaded as a PDF or sent to accounting as a logo-branded e-mail report.

The technical counterpart of step five is the cost field returned in every response — not an estimate, but the realized amount of that request:

{
  "id": "chatcmpl-...",
  "model": "openai/gpt-5.6-luna",
  "usage": {"prompt_tokens": 1984, "completion_tokens": 291},
  "cost": 0.00056
}

On the integration side the only thing that changes is base_url: the endpoint follows the OpenAI schema exactly, so existing SDK code works as-is, and the team can experiment without writing code in the in-panel Playground. Your contract counterparty is Onysoft Veri Merkezi A.Ş. (İzmir), established in Türkiye — also the accountable party of your KVKK data-processing agreement; details in the KVKK-compliant AI guide.

How Are Budget Overruns and Surprise Invoices Eliminated?

The prepaid-balance model carries no open-ended spending commitment, and the system never forwards a request the balance cannot cover. The mechanic: before every request, the estimated cost is computed with a 1.2x buffer and checked against your balance; if insufficient, the request returns a 402 error before it ever leaves for the provider. Encountering an unexpected amount at month-end is structurally impossible — when the balance runs out the service stops, and the account never goes negative.

The tools that push budget discipline down to team level should also be asked about at purchase time. On Onysoft they ship with the product:

• Per-key limits: Token limits per model can be defined for each API key — a test environment's key cannot burn the production budget.
• Filtered usage reports: Reports broken down by date, model, and status; PDF download and a logo-branded e-mail report deliverable straight to accounting.
• Per-request cost: Thanks to the cost field above, cost can be logged at request level in your own systems; the dashboard shows the lira equivalent.
• Automatic savings: Set the model field to onysoft/auto and OnyRouter routes cheap tasks to the economy class with free routing; only the selected model's usage is billed.

In purchasing language: no commitment, a hard ceiling; no estimates, realized cost per request.

Vendor Evaluation Checklist: What Should Purchasing Ask?

When evaluating an enterprise AI API vendor, ask for documented answers to each of the following; Onysoft's answers alongside:

• Invoicing: Are TRY e-Fatura/e-Arşiv invoices issued, and how is the type determined? — Automatically via live GİB VKN lookup; e-Fatura or e-Arşiv by taxpayer status.
• Contract counterparty: Is the counterparty a legal entity established in Türkiye? — Onysoft Veri Merkezi A.Ş., İzmir; contract under Turkish law, a concrete KVKK counterparty.
• Tax: Does the purchase raise a reverse-charge VAT/withholding agenda? — Not with a domestic TRY invoice (confirm with your tax advisor).
• Price transparency: Are prices published openly, and is per-request cost returned? — Live catalog + the cost field in every response.
• Budget control: Is there a spending ceiling and a limit mechanism? — Prepaid balance, pre-request check, per-key limits.
• Reporting: Can accounting get usable breakdowns? — Filtered reports, PDF, logo-branded e-mail.
• Support and continuity: Turkish-language support and verifiable partnerships? — 24/7 Turkish support; Anthropic Claude Partner Network membership is an independently verifiable signal.
• Exit cost: What happens if we leave? — The endpoint follows the OpenAI schema, so migrating is a base_url change; lock-in is low.

If you are an agency or software house planning to resell AI services under your own brand, also look at the partner program: a separate key/project per customer and your own margin. The fastest way to start evaluating is to open a free account and try the VKN lookup and Playground yourself; for the broader picture, the AI API guide is a good next stop.

Last updated: August 5, 2026 · Data: api.onysoft.com live catalog