I am working with this JSON data:

{
    "Data": {
        "Expires" : 0
    }
}

And I want to convert whatever is in the "Expires" key to a bool value.

Whether it is "true","false", "no", "yes", 0, 1, true, false

First I check if the value even exists.

 //DEFAULT
    $EXPIRES = false;

     if(array_key_exists('Expires', $DATA)) {

                if (isset( $DATA[ 'Expires' ] )) {
                    $EXPIRES = strtolower( clean_input( $DATA[ 'Expires' ] ) );
                    if (checkIfBoolean( $EXPIRES )) {
 //OK IT IS A BOOLEAN VALUE SET IT
                        $EXPIRES = filter_var(    $EXPIRES, FILTER_VALIDATE_BOOLEAN);
                    } else {
                        return array( "Code" => 0, "Error" => "Expires is not a boolean [0, 1]." );
                    }
                }
        }

//CAN'T TRUST THE USER, CLEAN THEIR INPUT
 function clean_input ( $data ) {
        $data = trim( $data );
        $data = stripslashes( $data );
        $data = htmlspecialchars( $data );

        return $data;
    }

//CHECK IF BOOLEAN

  function checkIfBoolean ( $string ) {
        $string = strtolower( $string );

        return ( in_array( $string, array( "true", "false", "1", "0", "yes", "no"), true ) );

    }

But when I check the variable

echo 'Expires: ' . $EXPIRES ? 'YES' : 'NO';

It always returns true.

What am I doing wrong.