Failed opening required '/vendor/autoload.php'

I have an Elastic Beanstalk with EC2 Instance (AWS).

When I call

require '/vendor/autoload.php';

or

require 'vendor/autoload.php';

I get the following error in the AWS logs:

Failed opening required '/vendor/autoload.php'&

Failed opening required 'vendor/autoload.php'

The folder structure for the vendor file location is

/home/ec2-user

 -composer.json

 -composer.lock

 /vendor

    - autoload.php

 /composer

In EC2 Public folder path is

/var/app/current/public/index.php

{I have even tried /home/ec2-user/vendor/autoload.php but I get the same

Failed opening required '/home/ec2-user/vendor/autoload.php'

The composer.json file says

{
    "require": {
        "phpmailer/phpmailer": "^6.1"
    }
}

What have I done wrong here?

Other failed openings include:

Failed opening required 'vendor/autoload.php'

Failed opening required '/var/www/html/public/vendor/autoload.php'