Can't connect to SQL database. For some reason, it works fine on one of my websites, but fails on another. Any clue?

Hi guys,

I use the following code, in connection.php which i include at the top of pages which I need to access a SQL database I've created.

I use this exact same code on another website which works completely fine. (See the console.log of this website to see the connection to the database: https://phlegethontic-flash.000webhostapp.com/art.php?cat=pottery

However, on a current project I am working on, the connection always fails. The error code is says is: SQLSTATE[HY000] [2002] No such file or directory. (See the console.log of this website to see how, even though the code for connection to the database is the same, on this website it doesn't connect.): http://www.mpowerelectrics.co.uk/areas.php

What is happening? Can anyone shed any light?

<?php
$servername = "localhost";
$username = "myusername";
$password = "mypassword";
$database = "mydatabase";

try {
    $conn = new PDO("mysql:host=$servername;dbname=$database", $username, $password);
    // set the PDO error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
      echo '<script>console.log("Connected successfully")</script>'; 
    } catch(PDOException $e) {    
    echo '<script>console.log("Connection failed: "' . $e->getMessage() . ')</script>'; 
    }