Li Su
Meanwhile, one of the imperial generals, Li Su the military governor of Tangsuideng Circuit (唐隨鄧, headquartered in modern Zhumadian) was planning a surprise attack on Zhangyi's capital Cai Prefecture (). When Li Su reported this plan to Pei, Pei approved of it. In winter 817, Li Su launched his attack and captured Cai Prefecture, taking Wu Yuanji captive and delivering him to Chang'an. When Pei subsequently arrived at Cai Prefecture, Li Su waited by the road to be ready to pay proper respect to Pei by military ceremony. Pei initially, in humility, wanted to avoid having Li Su bow to him, but Li Su pointed out that it was proper for them to demonstrate the proper etiquette for the imperial army before the surrendered soldiers and people of Cai Prefecture. Pei thus agreed.