How to upload dynamically generated file to S3 bucket using lambda with PHP?

Using bref as PHP serverless framework.

Problem:

Unable to upload the dynamically generated file to S3 bucket from Lambda using PHP. In CloudWatch, there is no any error.

Code:

serverless.yml

service: lambdaToS3

provider:
    name: aws
    region: ap-southeast-2
    runtime: provided.al2
    #stage: prod
    profile: default
    iam:
        role:
            statements:
                - Effect: Allow
                  Action:
                    - 's3:GetObject'
                    - 's3:PutObject'
                    - 's3:GetObjectAcl'
                    - 's3:PutObjectAcl'
                  Resource:
                    - 'arn:aws:s3:::*/*'

plugins:
    - ./vendor/bref/bref

functions:
    lambdaToS3:
        handler: index.php
        description: ''
        layers:
            - ${bref:layer.php-74}
        events:
            - httpApi: '*'

# Exclude files from deployment
package:
    patterns:
        - '!tests/**'
        - '!tmp/**'

index.php

comments are output when executing a file using HTTP GateWay

In this file, I am generating a simple text file in /tmp/ folder and trying to upload it to the S3 bucket with two different attributes, SourceFile or Body. None of them working.

<?php declare(strict_types=1);

ini_set('display_errors', "1");
ini_set('display_startup_errors', "1");
error_reporting(E_ALL);

require __DIR__ . '/vendor/autoload.php';

use Aws\S3\S3Client;
use Bref\Logger\StderrLogger;


    $logger = new StderrLogger();

    $s3client = new S3Client([
        'scheme' => 'http',
        'version' => '2006-03-01',
        'region' => 'ap-southeast-2',
        'output' => 'JSON'
    ]);

    $bucket = 'bucketname';
    
    $file = "/tmp/newfile.txt";
    $myfile = fopen($file, "w") or die("Unable to open file!");
    $txt = "John Doe\n";
    fwrite($myfile, $txt);
    $txt = "Jane Doe\n";
    fwrite($myfile, $txt);
    fclose($myfile);

    echo "<pre>"; print_r("File Exist: ". file_exists($file)); echo "</pre>"; // 1
    echo "<pre>"; print_r(" ================ "); echo "</pre>"; 
    echo "<pre>"; print_r(file_get_contents($file)); echo "</pre>"; // we can get content using this method.
    echo "<pre>"; print_r(" ================ "); echo "</pre>"; 

    // Put on S3 using SourceFile
    $result = $s3client->putObject([
        'Bucket' => $bucket,
        'Key' => "AWS_LAMBDA_S3.txt",
        'SourceFile' => $file,
        'ACL' => 'public-read',
    ]);

    echo "<pre>"; print_r("File Upload: " . json_encode($result)); echo "</pre>"; 

    // Put on S3 using Body
    $myfile = fopen($file, "rb");
    $result = $s3client->putObject([
        'Bucket' => $bucket,
        'Key' => "AWS_LAMBDA_S3_BODY.txt",
        'Body' => $myfile,
        'ACL' => 'public-read',
    ]);

    echo "<pre>"; print_r("File Upload: " . json_encode($result)); echo "</pre>"; 
    exit;

Regarding policy: Once the function deploy to AWS Lambda, we got a following policy for the role

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": [
                "logs:CreateLogStream",
                "logs:CreateLogGroup"
            ],
            "Resource": "arn:aws:logs:ap-southeast-2:xxxx:log-group:/aws/lambda/lambdaToS3-dev*:*"
        },
        {
            "Sid": "VisualEditor1",
            "Effect": "Allow",
            "Action": [
                "s3:PutObject",
                "s3:GetObjectAcl",
                "s3:PutObjectAcl"
            ],
            "Resource": "*"
        },
        {
            "Sid": "VisualEditor2",
            "Effect": "Allow",
            "Action": [
                "sqs:DeleteMessage",
                "sqs:ReceiveMessage",
                "sqs:GetQueueAttributes",
                "logs:PutLogEvents"
            ],
            "Resource": [
                "arn:aws:logs:ap-southeast-2:xxxx:log-group:/aws/lambda/lambdaToS3-dev*:*:*",
                "arn:aws:sqs:ap-southeast-2:xxxx:xxxx"
            ]
        }
    ]
}