Inconsistent error message for invalid model depending on API key

[dandv]

This is an issue with the Messages API rather than the SDK: attempting to use an invalid model identifier results in different error messages, depending on the API key being specified.

const response = await fetch('https://api.anthropic.com/v1/messages', {
  method: 'POST',
  headers: {
    'x-api-key': 'sk-ant-api03-H8yfz...-Q7161AAA',
    'anthropic-version': '2023-06-01',  // required by the Messages API
  },
  body: JSON.stringify({
    messages: [{ role: 'user', content: 'Hello' }],
    max_tokens: 4096,  // required, maximum
    model: 'invalid-model',
  }),
});
console.log(await response.json());

With the API key above, which I obtained from my Anthropic console, I see the following error:

{
  "type": "error",
  "error": { "type": "not_found_error", "message": "model: invalid-model" }
}

With a different API key, sk-ant-api03-1WH_3x...-ONyGHQAA, provided by @zack-anthropic, I see a different error message when running the same code:

{
  "type": "error",
  "error": { "type": "not_found_error", "message": "Not found" }
}

Related: #517