Of course you can't graft. The two plants belong to different families and genera, and the premise of grafting is that the two plants belong to the same family and genus. Longan belongs to the genus Longan of Sapindaceae, but belongs to the genus Clausena of Rutaceae. In order to successfully graft wampee, at least plants belonging to the same family and genus should be used.
All species of Clausena:
Ganghuangpi
Yellow bark of tooth leaf
Smooth yellow skin
Hainan wampee
Hubei wampee
wampee
False yellow skin
Dunn Huangpi Variety Zhongguo Coffee
Yellow bark of hairy leaves.
Clausena tenuifolia
Yellow skin of fragrant flower
Xiaohuangpi
Huangpi in Yunnan