What steps can be taken to troubleshoot issues with $_GET[$var] in PHP?

When troubleshooting issues with $_GET[$var] in PHP, it is important to check if the variable $var is properly set in the URL query string. Make sure that the variable is correctly spelled and encoded. Additionally, sanitize the input to prevent any security vulnerabilities.

// Check if the variable is set and sanitize the input
$var = isset($_GET['var']) ? htmlspecialchars($_GET['var']) : '';