OpenAI via x402: classify incoming business enquiries

On this page

We investigated a small, useful OpenAI task: classifying business enquiries into sales, support and billing. We checked the GPT-4o Mini route offered by x402engine and submitted a request to its free quote endpoint. Below, we share the exact input, the price it returned and the routing checks we'd use in a first trial.

That gives you a concrete starting point for assessing the cost and integration. It doesn't establish classification accuracy: we obtained the quote without purchasing the model's answer.

The access path is x402engine, a third-party gateway. Its service record names OpenRouter as the upstream provider. OpenAI's model documentation describes GPT-4o Mini as a small model for focused tasks, including intent classification. This route is separate from a direct OpenAI account or ChatGPT subscription.

Give the model one decision

Start with three queues: sales, support and billing. Ask for the category and a short reason. For an initial trial, a person can compare those answers with how the business would actually route the messages.

A sensible input is the enquiry text. Names, account identifiers and the full email history usually add little to this particular decision. If a message contains two distinct requests, your routing rule needs to say whether to choose a primary queue or refer it for review.

The exact request and its quote

Save this JSON as request.json:

{
  "messages": [
    {
      "role": "user",
      "content": "Classify this enquiry as sales, support, or billing. Return the category and one sentence explaining it. Enquiry: Please resend the invoice for August."
    }
  ],
  "max_tokens": 100
}

The model endpoint is POST https://x402engine.app/api/llm/gpt-4o-mini. To price the same body without buying a response:

curl https://x402engine.app/api/llm/gpt-4o-mini/quote \
  -H 'Content-Type: application/json' \
  --data-binary @request.json

On 7 September 2026, our free quote request returned $0.002685 USD, with an output budget of 100 tokens. At that unchanged quote, 1,000 identical requests would total $2.685. That is arithmetic on one observed quote, not a measured production bill: message length, output limits and gateway pricing can change it.

The paid route and request fields are documented in the gateway API schema. Use its x402 client instructions for the payment step. The quote command above does not purchase the model answer.

What a useful answer looks like

For the sample, the acceptance target is billing, with a reason such as “The sender is asking for an existing invoice.” This is our expected answer, not an observed paid response.

The downstream system should accept only the permitted categories. Asking for a label in a prompt does not guarantee the model will obey it. Missing labels, extra prose and ambiguous requests need an explicit handling rule before labels start driving work automatically.

Try a small set of enquiries that represent the actual inbox: a new quote request, a fault report, an invoice question and a message containing both a service problem and a payment dispute. Record the intended queue before running the trial. Count incorrect routing separately from requests referred for review; otherwise a system that guesses everything can appear more useful than it is.

Where this purchase fits

This buys a classification step. Your inbox integration still retrieves messages and routes them. It could sit inside fixed automation or an agent workflow, depending on who selects the next action.

The gateway is worth investigating when the surrounding software already makes x402 purchases. If your business already uses a direct OpenAI integration, compare the gateway's quote, data handling and operational benefit with that existing route. A different payment method alone does not make classification better.

The useful next step is the labelled enquiry trial, with success defined by correct routing rather than fluent explanations.