How to initialize a function via composer?

Question

Composer

Created a simple library via composer with one function:

namespace ing;
function amocrmErrors ($getCode, $getMessage,$domen){
  
  $data = array(
  'getCode' => $getCode, 
  'getMessage' =>$getMessage,
  'domen' => $domen	
  );
  
  $url = 'любой урл';
    $ch = curl_init($url);
    $encodedData = $data;

    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $encodedData);
  curl_setopt($ch, CURLOPT_USERAGENT,'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.154 Safari/537.36');  
    curl_setopt($ch, CURLOPT_HTTPHEADER, array('application/x-www-form-urlencoded'));
    curl_exec($ch);
    curl_close($ch);    
}

composer.json file

{
    "name": "ing/amolib",
    "description": "lib",
    "type": "library",
  "license": "MIT",
  
    "authors": [
        {
            "name": "ing",
            
        }
    ],	
    "minimum-stability": "dev",
    "prefer-stable": true,	
  "autoload": {
    "psr-4": {
            "ing\\": "src"        
    }
  },
    "require-dev": {
  "ing/amolib" : "dev-master"	
  },


  "require": {
        "php": ">=5.3.0"
}

}

When declaring a function: I get an
amocrmErrors($getCode, $getMessage,$domen );
error: Fatal error: Uncaught Error: Call to undefined function amocrmErrors() in..
Where am I wrong? Or do you need to work through classes through composer?
Thank you!