PHP connecting to Bedrock model and having issues with InvokeModel

There are a few issues with your code that are causing the error you're encountering:

1. You're using the wrong client for invoking the model. Instead of BedrockClient, you should be using BedrockRuntimeClient. The BedrockClient is for managing Bedrock resources, while BedrockRuntimeClient is for invoking models.

2. The region you're using (ap-southeast-2) may not support the Claude 3 Haiku model. Make sure to check which regions support the model you're trying to use.

3. The format of your request body is incorrect for the Claude 3 model. Claude 3 uses the Messages API, which requires a different structure.

Here's a corrected version of your code:

require 'vendor/autoload.php';

use Aws\BedrockRuntime\BedrockRuntimeClient;

$bedrockRuntime = new BedrockRuntimeClient([
    'region' => 'us-east-1', // or another region that supports Claude 3
    'version' => 'latest',
    'credentials' => [
        'key'    => 'X',
        'secret' => 'X',
    ],
]);

$response = $bedrockRuntime->invokeModel([
    'modelId' => 'anthropic.claude-3-haiku-20240307-v1:0',
    'contentType' => 'application/json',
    'accept' => 'application/json',
    'body'    => json_encode([
        'anthropic_version' => 'bedrock-2023-05-31',
        'max_tokens' => 1000,
        'messages' => [
            [
                'role' => 'user',
                'content' => 'Write me a Haiku'
            ]
        ]
    ]),
]);

$result = json_decode($response['body']->getContents(), true);
echo $result['content'][0]['text'];

Make sure you have the latest version of the AWS SDK for PHP installed. Also, double-check that you have been granted access to the Claude 3 model in your AWS account and that you're using a supported region for that model.

If you continue to face issues, verify your IAM permissions include the necessary actions to invoke models in Amazon Bedrock, specifically the "bedrock:InvokeModel" and "bedrock:InvokeModelWithResponseStream" actions.
Sources
Resolve InvokeModel API error in Amazon Bedrock | AWS re:Post
Bedrock API invocation error - on demand throughput isn's supported | AWS re:Post
Accessing Amazon Bedrock Claude-3-Haiku and Claude-3-Sonnet models via Lambda Functions | AWS re:Post