Validate a text field in contact form 7 and its not working

Here is my code , but its not working

add_filter( 'wpcf7_validate_text', 'custom_text_validation_filter', 10, 2 );

function custom_text_validation_filter( $result, $tag ) {
$tag = new WPCF7_Shortcode( $tag );     
if ('couponcode' == $tag->name) {
$the_value = $_POST[$name];
        if($the_value!="abc")
        {
$result->invalidate( $tag, "Invalid Coupon Code" );
        }
    }

    return $result;
}

Any Suggestion please ...Help me through it

via Chebli Mohamed