PHP - wp-testing addon

wp-add.php

//https://mailme.dev.cc/?x=1&a=1&b=2&c=3&d=4
add_action ('wp_loaded', 'my_custom_redirect');
function my_custom_redirect() {
    if(!empty($_GET['x'])){

		//set variables from get
		$a = sanitize_text_field( $_GET['a'] );
		$b = sanitize_text_field( $_GET['b'] );
		$c = sanitize_text_field( $_GET['c'] );
		$d = sanitize_text_field( $_GET['d'] );

		//send results to admin
		$redirect = site_url().'/privacy-policy?a='.$a.'&?b='.$b.'&?c='.$c.'&?d='.$d;
		$to = '[email protected]';
		$subject = 'New submission from form';
		$headers = array(
			'From: <[email protected]>' . "\r\n",
			'Cc: [email protected]' . "\r\n",
			"MIME-Version: 1.0" . "\r\n",
			"Content-type:text/html;charset=UTF-8" . "\r\n",
		);
		$message = 'form data: '.$redirect;

		wp_mail( $to, $subject, $message );

        wp_redirect($redirect);
        exit;
	}
	
	//The results page
	if(!empty($_GET['y'])){
		//set variables from get
		$a = sanitize_text_field( $_GET['a'] );
		$b = sanitize_text_field( $_GET['b'] );
		$c = sanitize_text_field( $_GET['c'] );
		$d = sanitize_text_field( $_GET['d'] );

		//send results to admin
		$redirect = site_url().'/privacy-policy?a='.$a.'&?b='.$b.'&?c='.$c.'&?d='.$d;
		$to = '[email protected]';
		$subject = 'Your results';
		$headers = array(
			'From: <[email protected]>' . "\r\n",
			'Cc: [email protected]' . "\r\n",
			"MIME-Version: 1.0" . "\r\n",
			"Content-type:text/html;charset=UTF-8" . "\r\n",
		);
		$message = 'view your results: '.$redirect;

		wp_mail( $to, $subject, $message );
	}
}

/*
user completes form and redirected to results page with x param
email input box
post to self and append y
echo message to confirm
*/