Return structured JSON

const response = await client.chat.completions.create({
  model: "gpt-5.4-mini",
  messages: [
    { role: "system", content: "Extract the support request into the supplied schema." },
    { role: "user", content: "My invoice has the wrong company name." },
  ],
  response_format: {
    type: "json_schema",
    json_schema: {
      name: "support_request",
      strict: true,
      schema: {
        type: "object",
        properties: {
          category: { type: "string", enum: ["billing", "technical", "account"] },
          summary: { type: "string" },
        },
        required: ["category", "summary"],
        additionalProperties: false,
      },
    },
  },
});

const result = JSON.parse(response.choices[0].message.content);