What potential issues can arise when transferring a website with a self-written CMS using PHP and MySQL to a different hosting provider with different PHP versions?

When transferring a website with a self-written CMS using PHP and MySQL to a different hosting provider with different PHP versions, potential issues can arise due to compatibility issues between the PHP versions. One common issue is deprecated functions or syntax that may cause the website to break or not function properly. To solve this issue, it is important to update the codebase to use functions and syntax that are compatible with the PHP version on the new hosting provider.

// Update deprecated functions to their modern equivalents
// For example, replace mysql_connect with mysqli_connect

$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Connected successfully";

// Close connection
mysqli_close($conn);