Why Mysqli Database Connection not Working Inside a Method or a Function in PHP

Sometimes, I have faced some issues when calling to function inside PHP script, The database connection not working inside the method/function, In case , it will work in MySQL but In the case of Mysqli Connection, we need to pass the connection object as a parameter.

<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "dynamic_field"; 

// Create connection

$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}

<?php

$servername = "localhost";

$username = "root";

$password = "";

$dbname = "dynamic_field";

// Create connection

$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection

if ($conn->connect_error) {

die("Connection failed: " . $conn->connect_error);

}

Suppose I have a function below example you can understand easily.

<?php 

function CheckEmail($link,$emailId){

//Do Some Code

}

// Calling the function 

CheckEmail($conn, $email);

?>

<?php

function CheckEmail($link,$emailId){

//Do Some Code

}

// Calling the function

CheckEmail($conn, $email);