According to Ennin's Diary, Chang Pogo(張保皐) had played an active part in overseas trade and founded a Buddhist cloister, which is called Fahuayuan(法華院) in DengZhou(登州) about 828. On the basis of the Buddist monasteries in Tang(唐) China, I tried to examine the practical roles of the Fahuayuan with overseas trade.
The Fahuayuan had many unofficial names, the cloister was clearly not approved from the Tang regime, On the other hand, it was located near sea and very useful to the official trade and diplomacy between the Silla(新羅) and the Tang regime. Because of that, the existence of the cloister could be gotten tacit approval from the Tang regime, and Chang Pogo used it as a strong business foothold in china.
The Fahuayuan had performed severla practical roles for Chang Pogo's overseas trade. It was a good hotel for foreign traders and diplomatic officials, and had a role administrative affairs for foreign trader and monk to entry into China. Moreover, this cloister had many estates itself, and could provide trading ships with food. Accordingly, the managementof the cloister got be achieved by common persons.
I think the Fahuayuan was a energetic cloister while Chang Pogo had active overseas trade. However, the cloister was abolished in accordance with the HuiChang(會昌) Persecution in 844.
This means that it was not seceded from the authority of the Tang regime.