How to make transparency for webp in php?

Question

PHP

Good day, I am converting from the format of incoming images to webp, but unfortunately, for some reason, transparency is not saved in webp, although it supports it.
Tell me how to fix the situation?

function createWebpImage2($link,$name){
    if(file_exists($link)){
        $a = exif_imagetype($link);
        switch($a){
            case 1:
                $source =  imagecreatefromgif($link);
                break;
            case 2:
                $source = imagecreatefromjpeg($link);
                break;
            case 3:
                $source =  imagecreatefrompng($link);
                break;
            default: $source=false;
        }
    }

    else{
        return false;

    }
        imagealphablending($source, false);
        imagesavealpha($source, true);
        imagewebp($source,$name.'.webp');
        imagedestroy($source);
}