trying to do a call with the following code and always I get back the same response

            $PROJECT_ID = "test123";
            $LOCATION = "us-central1";
            //$MODEL = "gemini-1.5-pro-preview-0409";
            $MODEL = "claude-3-haiku@20240307";
            $formattedEndpoint = PredictionServiceClient::projectLocationPublisherModelName($PROJECT_ID, $LOCATION, 'anthropic', $MODEL);
            Log::info($formattedEndpoint);
            $predictionServiceClient = new PredictionServiceClient([
                'apiEndpoint' => $LOCATION.'-aiplatform.googleapis.com',
            ]);

            $payload = [
                "anthropic_version" => "vertex-2023-10-16",
                "messages" => [["role" => "user", "content" => "Send me a recipe for banana bread."]],
                "max_tokens"        => 1000,
                "stream"            => false,
                //"temperature"       => floatval(env('CLAUDE_TEMPERATURE')),
            ];

$httpBody = new HttpBody();
            $httpBody->setContentType('application/json; charset=utf-8');
            $httpBody->setData(json_encode($payload));

            $request = (new RawPredictRequest)
                    ->setEndpoint($formattedEndpoint)
                    ->setHttpBody($httpBody);

            $response = $predictionServiceClient->rawPredict($request);

I also tried creating a new Struct() with the entire payload there but I always get the same validation error:

{
    "message": "messages: Field required",
    "code": 400,
    "status": "UNRECOGNIZED_STATUS",
    "details": []
}

Tried all kind of ways to send that messages parameter but always same result. I must be missing something simple here.