OpenAI GPT-4 API error: "The model: gpt-4 does not exist"

I have code as below, it works perfect with model gpt-3.5-turbo but not with gpt-4:

$your_prompt = "Prompt...."

// GPT-4 API call
$ch = curl_init();

curl_setopt($ch, CURLOPT_URL, 'https://api.openai.com/v1/chat/completions');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POST, 1);

$headers = array();
$headers[] = 'Content-Type: application/json';
$headers[] = 'Authorization: Bearer [API-KEY]';
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

$data = json_encode(array('model' => 'gpt-3.5-turbo', 
                          'messages' => array(
                                            array('role' => 'system', 'content' => 'Your system message here'), 
                                            array('role' => 'user', 'content' => $your_prompt))));

curl_setopt($ch, CURLOPT_POSTFIELDS, $data);

$result = curl_exec($ch);
echo $result."<br>";

if (curl_errno($ch)) {
    echo 'Curl Error:' . curl_error($ch) . "\n<br>";
} else {
    echo "API call successful.\n<br>";
    echo "API response: \n<br>";
    print_r(json_decode($result, true));
    echo "\n";
}
curl_close($ch);

$response = json_decode($result, true);
$text = $response['choices'][0]['message']['content'];

echo "OutputGPT" . $text . "\n<br>";

When I'm using gpt-4 I get:

Processing prompt: what is a wether today in Warsaw Poland
{ "error": { "message": "The model: `gpt-4` does not exist", "type": "invalid_request_error", "param": null, "code": "model_not_found" } }
API call successful.
API response:
Array ( [error] => Array ( [message] => The model: `gpt-4` does not exist [type] => invalid_request_error [param] => [code] => model_not_found ) ) OutputGPT

I have tried also with others models like gpt-3.5-turbo-0613 and it works to, but not for gpt-4 as well as for gpt-4-0613. Nevertheless it should based on https://platform.openai.com/docs/models/gpt-4

Since July 6, 2023, the GPT-4 8k models have been accessible through the API to those users who have made a successful payment of $1 or more through the OpenAI developer platform.

Take a look at the official OpenAI documentation.

For the GPT-4 models, you can see the following notice:

While for the GPT-3.5 models, there's no such notice:

As stated in the official OpenAI article:

> On July 6, 2023, we gave access to the GPT-4 8k API to all API users
> who have made a successful payment of $1 or more. We plan to open up
> access to all developers soon, and then start raising rate-limits
> after that depending on compute availability.
>
> We are not currently granting access to the GPT-4 32k API at this time, but it will be made available at a later date.
>
> For API accounts created after August 18, 2023, you can get instant
> access to GPT-4 after purchasing $0.50 worth or more of pre-paid
> credits. You can read about prepaid billing here.

Additional notes:

• Can I get instant access to GPT-4 8k models via API even if I haven't spent at least $1 in the past? Yes, if your account was created after August 18, 2023, and you purchase $0.50 worth or more of pre-paid credits.
• Why can't I access GPT-4 32k models via API? Only the GPT-4 8k models are available via API. Access to the GPT-4 32k models via API will be made available at a later date.
• Why don't I get access to the GPT-4 8k models via API even though I paid $20 for my ChatGPT Plus subscription? OpenAI API usage is not included in the ChatGPT Plus subscription.