Sorry my bad. It's working and that I didn't recognize the quest item in my bag. Thanks for everything.
PS: sorry for my poor Engish as I'm not a native English speaker.
Wowhead quest link:
WoW Freakz quest link: https://www.wow-freakz.com/quest_helper.php?quest=40131&name=stonehide-leather-sample
Bug description: I purchased skinning from freakz shop, but the ...