The button loop has come loose — I can't fasten it.
Tips
culture
The fabric loop that catches a 盘扣 (pánkòu, knotted Chinese button) on a 旗袍 (qípáo) or 唐装 (tángzhuāng). 襻 by itself means a loop or strap of cloth — you'll also see it in 鞋襻 (shoe strap) and 裤襻 (belt loop).