警告：move_uploaded_file（）：无法将'file'移动到'folder'

I try to upload an image to a directory on localhost.

Here is the part in my php file, which causes the error:

if (move_uploaded_file($tmp_name, "/Users/sandro/Documents/bildgalerie/uploads")) {
    echo "The file " . basename($filename) . " has been uploaded";
} else {
    echo "error";
}

If I load the page, I get the following:

Warning: move_uploaded_file(): Unable to move '/private/var/folders/np/sln14hvn3tsbzc4kpjjtp17c0000gn/T/phppJbFJK' to '/Users/sandro/Documents/bildgalerie/uploads' in /Users/sandro/Documents/bildgalerie/control/upload.php on line 31