Ubuntu – DynamoDB + PHP using aws sdk giving itemGet() schema mismatch errors

First, allow me to predicate that I am a relative noob to much of this, and self-taught in the rest.

I have a simple DynamoDB table set up named ‘NeedsSystemData’ that includes one record with the following Keys/Attributes:

ResidentUUID (Partition key) = b4f1eda1-bf41-4a25-b86e-bb03c3c68099 (string)
ResidentName (Sort key) = Galathir Darkstone (string)
HUDKey = 704b24e5-3471-f67a-4395-9ab65a5a4031 (string)
HUDurl = http://simhost-02134e0505318f492.agni.secondlife.io:12046/cap/6bcbd734-d6cd-c921-4cec-cd637e3c3613 (string)

I have one PHP script with this code:

<?php
    // slcom.php

    // Prepping for DynamoDbClient
    require 'vendor/autoload.php';
    require 'credentials.php';

    use AwsDynamoDbDynamoDbClient;
    use AwsDynamoDbExceptionDynamoDbException;
    use AwsDynamoDbMarshaler;

    // Create a DynamoDBClient
    $client = new DynamoDbClient([
        'region' => $region,
        'version' => 'latest',
        'credentials' => [
            'key' => $access_key,
            'secret' => $secret_key,
        ],
    ]);

    // Global variable for table name
    $GLOBAL_TABLE_NAME = 'NeedsSystemData';

    try {
        $response = $client->scan([
            'TableName' => $GLOBAL_TABLE_NAME,
            'Limit' => 1, // Limit the scan to return only one item
        ]);

        $items = $response['Items'];
        if (!empty($items)) {
            $firstRecord = $items[0];
            echo 'First Record:' . PHP_EOL;
            echo 'ResidentUUID: ' . $firstRecord['ResidentUUID']['S'] . PHP_EOL;
            echo 'ResidentName: ' . $firstRecord['ResidentName']['S'] . PHP_EOL;
            echo 'HUDKey: ' . $firstRecord['HUDKey']['S'] . PHP_EOL;
            echo 'HUDurl: ' . $firstRecord['HUDurl']['S'] . PHP_EOL;
        } else {
            echo 'No records found in the table.' . PHP_EOL;
        }
    } catch (Exception $e) {
        echo 'Error: ' . $e->getMessage() . PHP_EOL;
    }

?>

That code generates this output:

First Record: ResidentUUID: b4f1eda1-bf41-4a25-b86e-bb03c3c68099 ResidentName: Galathir Darkstone HUDKey: 704b24e5-3471-f67a-4395-9ab65a5a4031 HUDurl: http://simhost-02134e0505318f492.agni.secondlife.io:12046/cap/6bcbd734-d6cd-c921-4cec-cd637e3c3613

So far, so good. However, when I try to move long to using a getItem(), I have some problems. That code is:

<?php
    // slcom.php

    echo 'Opening Table' . PHP_EOL;

    // Prepping for DynamoDbClient
    require 'vendor/autoload.php';
    require 'credentials.php';

    use AwsDynamoDbDynamoDbClient;
    use AwsDynamoDbExceptionDynamoDbException;
    use AwsDynamoDbMarshaler;

    // Create a DynamoDBClient
    $client = new DynamoDbClient([
        'region' => $region,
        'version' => 'latest',
        'credentials' => [
            'key' => $access_key,
            'secret' => $secret_key,
        ],
    ]);

    // Global variable for table name
    $GLOBAL_TABLE_NAME = 'NeedsSystemData';

    try {
        // Use the specific ResidentUUID you want to retrieve
        $sampleResidentUUID = 'b4f1eda1-bf41-4a25-b86e-bb03c3c68099';

        $response = $client->getItem([
            'TableName' => $GLOBAL_TABLE_NAME,
            'Key' => [
                'ResidentUUID' => ['S' => $sampleResidentUUID],
            ],
        ]);

        $item = $response['Item'];
        if (!empty($item)) {
            echo 'First Record:' . PHP_EOL;
            echo 'ResidentUUID: ' . $item['ResidentUUID']['S'] . PHP_EOL;
            echo 'ResidentName: ' . $item['ResidentName']['S'] . PHP_EOL;
            echo 'HUDKey: ' . $item['HUDKey']['S'] . PHP_EOL;
            echo 'HUDurl: ' . $item['HUDurl']['S'] . PHP_EOL;
        } else {
            echo 'No records found with the given ResidentUUID.' . PHP_EOL;
        }
    } catch (Exception $e) {
        echo 'Error: ' . $e->getMessage() . PHP_EOL;
    }
?>

The output from that code is:

Opening Table Error: Error executing "GetItem" on "https://dynamodb.us-east-2.amazonaws.com"; AWS HTTP error: Client error: `POST https://dynamodb.us-east-2.amazonaws.com` resulted in a `400 Bad Request` response: {"__type":"com.amazon.coral.validate#ValidationException","message":"The provided key element does not match the schema" (truncated...) ValidationException (client): The provided key element does not match the schema - {"__type":"com.amazon.coral.validate#ValidationException","message":"The provided key element does not match the schema"}

I have a feeling this is something stupidly simple that should be obvious… except for the afore-mentioned noobness. If someone less noob would help point me in the right direction, I would appreciate it.

In case it matters: The scripts are being run as index.php on an aws EC2 instance running Ubuntu 22.04.2 LTS (GNU/Linux 5.19.0-1028-aws x86_64).