White space issues in WordPress files, “error on line 2 at column 6: XML declaration allowed only at the start of the document” especially in functions.php and wp-config.php, can cause the readed “Headers already sent” error. This happens when there are spaces, line breaks, or invisible characters before the opening <?php tag or after the closing ?> tag.

Manual Fix (Recommended)

Before using a script, check these files manually:

1. Access your WordPress files via cPanel File Manager or FTP.
2. Open wp-config.php and functions.php (located in /wp-content/themes/your-theme/).
3. Remove any spaces or blank lines before <?php and after ?> (if the closing tag exists).
4. Save the files and check if the issue is resolved.

Automated Fix Using a Script

If manual removal doesn’t work, you can use a PHP script to clean up white spaces:

Step 1: Create a Fixer Script

1. In cPanel File Manager, navigate to your WordPress root directory (where wp-config.php is located).
2. Create a new file named whitespaceremove.php and paste this code:

<?php
function ___wejns_wp_whitespace_fix($input) {
	$allowed = false;
	$found = false;
	foreach (headers_list() as $header) {
		if (preg_match("/^content-type:\\s+(text\\/|application\\/((xhtml|atom|rss)\\+xml|xml))/i", $header)) {
			$allowed = true;
		}

		if (preg_match("/^content-type:\\s+/i", $header)) {
			$found = true;
		}
	}

	if ($allowed || !$found) {
		return preg_replace("/\\A\\s*/m", "", $input);
	} else {
		return $input;
	}
}
ob_start("___wejns_wp_whitespace_fix");
?>

Then open the index.php and add the line include('whitespaceremove.php'); right after the <?php tag