Can confirm it works on PW3 too, I had some issues with the included AWS SDK:
So just for trying something out because I couldn't figure out anything from the error, I switched to installing the Amazon SDK through composer to get the latest version of the SDK and I basically just had to change how the S3 client is initialized.
$this->client = new S3Client([
'version' => 'latest', //Hardcoded value, think this has to do with the SDK version?
'region' => 'us-east-2', //Hard coded value for now, could be a config field
'credentials' => [
'key' => $this->s3_key,
'secret' => $this->s3_secret,
],
]);
Also removed the require_once for the included SDK.